# Calibrating Test Kits - for non-Chemists



## plakat

IMO this needs to be a sticky. I would check but I am procrastinating doing homework.


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## Dave k

plakat said:


> IMO this needs to be a sticky.
> 
> 
> I second the motion


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## ColeMan

Sticky, sticky, sticky - 5 stars from me! Excellent work, Hoppy. Now that you've made this so simple, I'm going to have to find something else to do with my digital scale! :thumbsup:


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## plantbrain

It's sort of EI for test kit calibration.


Regards, 
Tom Barr


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## Hoppy

plantbrain said:


> It's sort of EI for test kit calibration.
> 
> 
> Regards,
> Tom Barr


I was planning to call it the Julia Child calibration plan.:icon_mrgr


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## jjp2

Nice work. Check the phosphate, it says to add KNO3 not kh2po4 or other compound


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## clmntch

*Thanks*

Thanks Hoppy...


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## Hoppy

jjp2 said:


> Nice work. Check the phosphate, it says to add KNO3 not kh2po4 or other compound


Thank you! I corrected it.


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## epicfish

manofmanyfish said:


> Humm...1/2 cup plus 3/4 cup = one cup.....that's like creating matter from nothing....that's cool. I smell a Nobel Prize...:icon_eek:


You mean making matter disappear?

1/2 + 3/4 = 1 1/4


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## Hoppy

manofmanyfish said:


> Humm...1/2 cup plus 3/4 cup = one cup.....that's like creating matter from nothing....that's cool. I smell a Nobel Prize...:icon_eek:


I ran this through Einstein's Relativity equations, and you are right. So I corrected it.


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## Hoppy

Yesterday I made some 4 dKH water, using 14 dKH water made from an ampule of lab standard water. When I used my KH test kit to measure the KH of that water, it said 3 dKH. So, that raised a lot of doubts in my mind about the KH test kits. Calibrating that kit is a much harder job. But, it finally occurred to me that I should be able to take advantage of a property of sodium bicarbonate to do that. The property is the solubility of NaHCO3 in water, which varies with temperature. I converted the graph of that solubility to read in solubility of carbonate instead of sodium bicarbonate, getting this graph:









The technique will be to start with distilled water, add a lot of baking soda to that, let it sit quietly on the kitchen counter (where else?) for an hour or so, with only very gentle stirring, to saturate the water with baking soda. It won't matter that my baking soda will contain some water in the crystal structure, since that water just joins the distilled water. Then I use a syringe to get a sample of that water, 1 ml, as closely as I can get, and quickly add it to enough distilled water to end up with 20 dKH water, by calculation. Then dilute that to get my standard solutions. Will this work? I know the saturated solution will be losing CO2 to the atmosphere, but if I do this rapidly I should still have saturated solution being added to the distilled water. Am I missing something?

If this will work, it is another way to make 4 dKH drop checker water.


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## tazcrash69

plakat said:


> IMO this needs to be a sticky. I would check but I am procrastinating doing homework.


I agree, great write up Hoppy. Thanks 

Stickified.


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## Hoppy

*Calibrating KH test kit*

KH Test Kit
This method, compliments of Cardinal's Keeper (http://www.plantedtank.net/forums/diy/178491-another-diy-4-dkh-solution.html)
(Note: You will need a whole gallon of distilled water to do this.)
1. Start with 6 cups of distilled water in a clean measuring container
2. Add 1/8 teaspoon Sodium Bicarbonate (baking soda, freshly opened) to the 6 cups of water and mix 
3. Pour out 3 cups of this mix and discard
4. Add back 3 cups of distilled water and mix
5. Pour out 3 cups of this mix and discard
6. Add back 3 cups of distilled water and mix
7. Pour out 1 cup of this mix and discard
8. Add back 1 cup of distilled water and mix
7. Water comes out to a 4 dKH solution
8. To make a 2 dKH solution, mix one cup of the 4 dKH solution with one cup of distilled water.
9. To make a 1 dKH solution, mix one cup of the 2 dKH solution with one cup of distilled water.


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## Regloh

Thanks Hoppy, 
I appreciate the work you put into this. I don't have an accurate scale to use other described methods, so this is making my day 
It actually is similar to what I do to add a known amount of Calcium and Magnesium to my water. Eventually I may have done the math myself some day, but now I'll just use your method


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## handyguy42

I m really happy..I appreciate the work you put into this. I don't have an accurate scale to use other described methods, so this is making my day thanks all...


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## houstonhobby

Hoppy,

I really appreciate this post. I don't understand the part about doing the calibration every time I use my kit. If I am using an API kit with little bottles of drops, what makes the kit results drift so much from week to week? Just asking for information you understand. I don't have the knowledge necessary to critique your statement.

Also, could I save the test tubes where I did the test, and use those to compare my colors against, instead of using the card that came with the test kit?

Thanks,
Rod


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## Hoppy

Oops, I'm very late seeing this. Sorry!

It isn't that the test kit results vary from day to day, it is that they are made with organic chemicals, with organic dyes, and those are not stable chemicals. Eventually they deteriorate. So, if your test kit sat on the dealer's shelf for a year before you bought it, or if the dealer allowed his store to get very hot for a few days, like over the weekend, the kits may never be accurate after you buy them. Then, if you are like me, you buy the kit, stash it under the aquarium and when you finally use it, you don't remember how long you have had it, so it may deteriorate on your shelf too. Now, add to that, that these are very cheap kits, so it is highly unlikely that there is good quality control on their manufacture.

Even if none of the above apply to you, just remember that professionals who do testing of any kind always calibrate their test equipment before use, or, at a minimum every few months. And, that calibration is done with an accuracy far better than the test equipment is designed to meet. No one who is paid to test things ever uses anything for measurements unless it is calibrated first and often. Even professional mechanics get their vernier calipers calibrated on a routine schedule.


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## wespastor

Thread Resurection!!!!!!:icon_eek:


Any new calibrations???

Thanks,
Wes


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## plantbrain

Ho hum............calibrated test kits for nutrients which are among the easiest things to add.....but not CO2 calibrations, light? Well, folks need a PAR meter, and reference bulb and distance, but light calibration is fairly easy as well.

Still, why do folks spend a lot of time, energy, $, effort etc on ferts, and not on light or CO2? Wanna be all precise and Scientific with ferts, then wing it with CO2/light?

My point is that light and CO2 are much larger factors in management. The same types of calibration rules apply to their measure that do to Test kits for NO3. Once CO2/light are correctly addressed for a management goal you have, then nutrients are really easy and have much less impact.

Still, folks should calibrate whenever they can if they want to feel the results are actually correct. If you prefer to guess, then why bother testing at all?
Do not even bother, do a decent water change and move on.

Better than guessing and not doing anything.

Regards, 
Tom Barr


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## Aquaticz

Hoppy to the rescue 
Well you have done it again _ thank you


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## Hoppy

wespastor said:


> Thread Resurection!!!!!!:icon_eek:
> 
> 
> Any new calibrations???
> 
> Thanks,
> Wes


None, and I don't expect to do any additional ones. Remember, the only purpose for doing this type of calibration is to find out if your test kit readings mean anything. The accuracy you can get this way is very limited. But, it is better than thinking your tank has 50 ppm of PO4 in it, when it really has less than 4 ppm. I don't use test kits at all now, and never did make much use of them, so this was mostly just a challenge for me. I did try to make 4dKH water using the method here, and it measured 3 dKH with my test kit. So, that "proves" that either this calibration method works, but with crude accuracy, which is what I aimed for, or it proves that my KH test kit readings are off. Being an optimist, I assume the former :icon_bigg


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## sbailiff

*Thank you!*

Thank you for this awesome calibration. I just think that it is still a little baffling to me. I don't know where to get No3 or the phosphate test product. Is there some obvious source? I am sorry for sounding stupid. 

Thank you. Steph


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## max chavez

ahhhhhh......what conflicting emotions I had this afternoon, when, after testing nitrates with a 'new' test kit for the last several months and not agreeing with the results, I picked up a galllon of distilled water and made some test solutions! Luckily, the results were very easy to read:
Tank water: yellow
10ppm standard: yellow
25ppm standard: yellow
50ppm standard: yellow

All exactly the same shade even! It was so simple! Now I know that my water is probably kinda close to 10-50ppm +/-50 or so. Thanks API/retailer

(and thank you Hoppy, for making the procedure so user friendly-no sarcasm)

I guess I'll just stick to those water changes, who knew?(well, Tom, I guess)


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## Whitebeam

This looks supurb, and is probably just what I need to help resolve the difference between my tap water (25ppm Nitrate) and the time for a critical water change (50ppm? Nitrate). Two questions please:

1) Can the reference solutions be kept for a few weeks, or will the colours deteriorate?

2) Any chance that somebody could translate the measurements in the recipes into SI units? Many of us don't use cups as volume measures and don't use volume measures (teaspoons) to precisely measure chemical powders.

Edit: Trying to answer 2) myself. Presumably the 'cups' used in the recipes are US cups, i.e. 236.6ml. Now, all I need to do is work out the weight of a teaspoon on Potassium Nitrate (etc)

Peter


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## Hoppy

Whitebeam said:


> This looks supurb, and is probably just what I need to help resolve the difference between my tap water (25ppm Nitrate) and the time for a critical water change (50ppm? Nitrate). Two questions please:
> 
> 1) Can the reference solutions be kept for a few weeks, or will the colours deteriorate?
> 
> 2) Any chance that somebody could translate the measurements in the recipes into SI units? Many of us don't use cups as volume measures and don't use volume measures (teaspoons) to precisely measure chemical powders.
> 
> Edit: Trying to answer 2) myself. Presumably the 'cups' used in the recipes are US cups, i.e. 236.6ml. Now, all I need to do is work out the weight of a teaspoon on Potassium Nitrate (etc)
> 
> Peter


I admit I didn't give any thought to the rest of the world where "cups" and "teaspoons" are not easy to measure. All I wanted to do was make it easy for someone with a typical American kitchen to determine if his/her test kit reading meant anything at all. A similar approach could be taken with common metric measuring equipment. I will leave it to you to enjoy working that out:biggrin:


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## Whitebeam

Hoppy said:


> I will leave it to you to enjoy working that out:biggrin:


A challenge! This is taking me back 28 years to my O-Level chemistry class - wow. Check my rusty theory here and then I'll try to work out 'kitchen' units later on ...

Looking at your NO3 example (1/4tsp in 4 cups):800ppm NO3 = 800mg/l NO3
Molecular mass of NO3 = 62.0, molecular mass KNO3 = 101.1
So: 800mg/l NO3 is equivalent to 800 x (101.1/62.0) = 1304.5mg/l KNO3​If this is right, and 4 cups = 946.4ml, then:Your 1/4 tsp KNO3 should weigh: 1304.5 * (946.4 / 1000.0) = 1234.5mg​Did I get it right, teacher? :icon_bigg

Peter


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## Hoppy

Whitebeam said:


> [/INDENT]Did I get it right, teacher? :icon_bigg
> 
> Peter


Unfortunately I didn't keep my scratch pad calculations. As I recall I used a round number for the mass of the fertilizer chemicals per teaspoon. It may have been 4 grams or 5 grams, but I can't recall for sure. So, I don't know if you got it right. It does look like you are using the right logic, so it is probably right.


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## ar0wan

max chavez said:


> ahhhhhh......what conflicting emotions I had this afternoon, when, after testing nitrates with a 'new' test kit for the last several months and not agreeing with the results, I picked up a galllon of distilled water and made some test solutions! Luckily, the results were very easy to read:
> Tank water: yellow
> 10ppm standard: yellow
> 25ppm standard: yellow
> 50ppm standard: yellow
> 
> All exactly the same shade even! It was so simple! Now I know that my water is probably kinda close to 10-50ppm +/-50 or so. Thanks API/retailer...


 
The bottle labeled #2 is not extra solution
it must be combined with #1 per the instructions to give correct readings


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## dobie832

The calibration solutions are usless as you used volume/volume. The volume of water will vary based on temp and the spoons of dry ferts can vary due to compaction differences. Any good lab will use weight/weight as they do not change.I suspect your solutions could vary by as much as 20%


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## wkndracer

dobie832 said:


> The calibration solutions are usless as you used volume/volume. The volume of water will vary based on temp and the spoons of dry ferts can vary due to compaction differences. Any good lab will use weight/weight as they do not change.I suspect your solutions could vary by as much as 20%


If you have a few minutes to make those corrected adjustments please post the results. It will be gratefully received.


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## Hoppy

dobie832 said:


> The calibration solutions are usless as you used volume/volume. The volume of water will vary based on temp and the spoons of dry ferts can vary due to compaction differences. Any good lab will use weight/weight as they do not change.I suspect your solutions could vary by as much as 20%


Read the first paragraph in: http://www.plantedtank.net/forums/f...rating-test-kits-non-chemists.html#post800225


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## Cactus Bastard

Hoppy said:


> I admit I didn't give any thought to the rest of the world where "cups" and "teaspoons" are not easy to measure. I will leave it to you to enjoy working that out:biggrin:


I did not even have to pull out my calculator, second google hit on "KNO3 reference solution" took me to a page that seems trustworthy enough :hihi: 
http://www.bestaquariumregulator.com/reference.htm
Here is a copy and paste from Rex's site (links sometimes change or go dead):

Here's a way to make 10, 20, 30 and 40 ppm NO3 reference solutions:

* Add 1.631 g of KNO3 to 1 L distilled or DI water. This makes a 1000 ppm NO3 solution. (It's really a 1000.29 ppm solution.)
* Add 2 mL of the 1000 ppm solution to 18 mL of distilled or DI water. This makes 20 mL of a 100 ppm NO3 solution.
* Add 15 mL of the 100 ppm solution to 15 mL of distilled or DI water. This makes 30 mL of a 50 ppm NO3 solution.

To make a 10 ppm NO3 solution:
* Add 2 mL of the 50 ppm solution to 8 mL of distilled or DI water. This makes 10 mL of a 10 ppm NO3 solution.

To make a 20 ppm NO3 solution:
* Add 4 mL of the 50 ppm solution to 6 mL of distilled or DI water. This makes 10 mL of a 20 ppm NO3 solution.

To make a 30 ppm NO3 solution:
* Add 6 mL of the 50 ppm solution to 4 mL of distilled or DI water. This makes 10 mL of a 30 ppm NO3 solution.

To make a 40 ppm NO3 solution:
* Add 8 mL of the 50 ppm solution to 2 mL of distilled or DI water. This makes 10 mL of a 40 ppm NO3 solution.

He also explains how to make reference solutions for testing phosphates:

Here's a way to make 1.0, 2.0, 3.0, 4.0 and 5.0 ppm PO4 reference solutions:

* Add 1.433 g of KH2PO4 to 1 L distilled or DI water. This makes a 1000 ppm PO4 solution. (It's really a 1000.09 ppm solution.)

To make 10 mL of a 100 ppm PO4 solution:
* Add 1 mL of the 1000 ppm solution to 9 mL of distilled or DI water.

To make 20 mL of a 10 ppm PO4 solution:
* Add 2 mL of the 100 ppm solution to 18 mL of distilled or DI water.

To make a 1.0 ppm PO4 solution:
* Add 1 mL of the 10 ppm solution to 9 mL of distilled or DI water. This makes 10 mL of a 1.0 ppm PO4 solution.

To make a 2.0 ppm PO4 solution:
* Add 2 mL of the 10 ppm solution to 8 mL of distilled or DI water. This makes 10 mL of a 2.0 ppm PO4 solution.

To make a 3.0 ppm PO4 solution:
* Add 3 mL of the 10 ppm solution to 7 mL of distilled or DI water. This makes 10 mL of a 3.0 ppm PO4 solution.

To make a 4.0 ppm PO4 solution:
* Add 4 mL of the 10 ppm solution to 6 mL of distilled or DI water. This makes 10 mL of a 4.0 ppm PO4 solution.

To make a 5.0 ppm PO4 solution:
* Add 5 mL of the 10 ppm solution to 5 mL of distilled or DI water. This makes 10 mL of a 5.0 ppm PO4 solution.


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## Hoppy

There are several posts in forums that tell how to use grams and liters to make reference solutions. My contribution was a way to do well enough using just what an average American kitchen would have - measuring spoons and cups.


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## Cactus Bastard

Yeah, the info is extremely accessible, but hadn't actually made it's way into _this_ thread, which happens to be a sticky on one of the largest planted tank forums out there. 

Cups and teaspoons are far more relevant to 90% of the members here, but a couple people had asked about alternative measurements, and I thought it would be a good idea to have both options listed in this one thread.


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## Hoppy

I updated the KH standard solution method here: http://www.plantedtank.net/forums/f...rating-test-kits-non-chemists.html#post801218


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## aadro

*Newbie issue: Non-standard issue of drop-cheker*



Hoppy said:


> KH Test Kit
> This method, compliments of Cardinal's Keeper (http://www.plantedtank.net/forums/diy/178491-another-diy-4-dkh-solution.html)
> (Note: You will need a whole gallon of distilled water to do this.)
> 1. Start with 6 cups of distilled water in a clean measuring container
> <.... selection deleted for brevity...>
> 8. To make a 2 dKH solution, mix one cup of the 4 dKH solution with one cup of distilled water.
> 9. To make a 1 dKH solution, mix one cup of the 2 dKH solution with one cup of distilled water.


Hi all of you, and Hoppy in particular. I am a newbie and want to do CO2 injection in an 80G planted aquarium. I don't want my plants to be completely slow-growing and low-tech, and I don't want them to be growing too vigorously either, as with 30ppm of CO2. [Yeah, I'm that Great Moderation guy! :redface:] So, I'm thinking I'll go for moderation, say about 15ppm of CO2, moderate lighting. I have two questions:

(1) Does this approach seem reasonable, or am I forgetting/ignoring something important?
(2) Now the more "techy" question. MOst standard drop-checkers, set up with 4dKH, turn green at 30ppm. This works fine for those who want to keep their tanks at 30ppm CO2, but it wouldn't work well for me. I need an indicator that'll tell me (say go from blue to green) at 15ppm instead of 30ppm. So, looking at Hoppy's above post, I thought, why don't I make a 2dKH solution to put in the drop checker? The charts [ http://freshwateraquariumplants.com/carbondioxidechart.html ] seem to say that 2dKH will get to pH=6.6 at about 15 ppm instead of 30ppm, so this should work for me, right? All I do is put 2dKH standard solution and a few drops of the indicator into the drop-checker, and voila! I calibrate CO2 to keep the solution green without going blue or yellow, just like everybody else does, but I'm keeping it at 15ppm, not 30ppm, right? What am I missing?

Thanks for your help in advance!

-aadro


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## Hoppy

aadro said:


> Hi all of you, and Hoppy in particular. I am a newbie and want to do CO2 injection in an 80G planted aquarium. I don't want my plants to be completely slow-growing and low-tech, and I don't want them to be growing too vigorously either, as with 30ppm of CO2. [Yeah, I'm that Great Moderation guy! :redface:] So, I'm thinking I'll go for moderation, say about 15ppm of CO2, moderate lighting. I have two questions:
> 
> (1) Does this approach seem reasonable, or am I forgetting/ignoring something important?
> (2) Now the more "techy" question. MOst standard drop-checkers, set up with 4dKH, turn green at 30ppm. This works fine for those who want to keep their tanks at 30ppm CO2, but it wouldn't work well for me. I need an indicator that'll tell me (say go from blue to green) at 15ppm instead of 30ppm. So, looking at Hoppy's above post, I thought, why don't I make a 2dKH solution to put in the drop checker? The charts [ http://freshwateraquariumplants.com/carbondioxidechart.html ] seem to say that 2dKH will get to pH=6.6 at about 15 ppm instead of 30ppm, so this should work for me, right? All I do is put 2dKH standard solution and a few drops of the indicator into the drop-checker, and voila! I calibrate CO2 to keep the solution green without going blue or yellow, just like everybody else does, but I'm keeping it at 15ppm, not 30ppm, right? What am I missing?
> 
> Thanks for your help in advance!
> 
> -aadro


That would work fine, but keep in mind that a drop checker with 4 dKH fluid will be "green" not at 30 ppm, but at something between about 20 and 40 ppm. There is a lot of built in uncertainty with this method, based on the limits of our eyes in seeing green as a specific color, and on the inaccuracy in measuring pH.

I experimented a lot with using a drop checker where yellow was the indication of the right amount of CO2. This was primarily for DIY CO2, where the battle is about getting enough CO2, not about avoiding too much CO2. I ended up using 1.7 dKH fluid. It worked pretty well for me when I was using it, but making 1.7 dKH fluid is hard to do without starting with a good, known KH solution. http://www.plantedtank.net/forums/showthread.php?t=129720


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## aadro

*Newbie question on non-standard drop-checker use*

Thanks Hoppy! That's useful. So, in that case, I'll be even "safer" using my method, so that if I use 2dKH instead of 4dKH, if the solution goes yellow, I'm less likely to overdose with CO2, although I realize from your comment that I am also likely to under-dose! May eventually need a more accurate meter of some sort!

Any ideas from anybody?


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## aadro

*Folloup up to Drop-Checker Question*

Apropos above "conversation" between Hoppy & Aadro:

Yup, I think I'm going to get myself two drop-checkers too!


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## Hoppy

I have tried 2 drop checkers numerous times, with various KH fluids in them, hoping that would improve the accuracy. It never did. The basic problem is the difficulty in judging the color of the solution - a slight mistake in judging what is "green" makes a big mistake in the ppm of CO2 you think you have. I ended up the happiest when I used yellow as the desired color, and DIY CO2 so I could be sure I wouldn't ever have too much CO2. Then I just tried to keep the DC color yellow, which was relatively easy.


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## markstr

Question: once I have the 4dkh solution here, do I just add to the drop checker or would I add a low PH solution say a drop or 2 to get the Dark Blue color as well into the drop checker and then wait a couple of hrs for correct readings ? I know you mentioned (which makes sense) in regards to "What is Green" to the eye. 



Hoppy said:


> KH Test Kit
> This method, compliments of Cardinal's Keeper (http://www.plantedtank.net/forums/diy/178491-another-diy-4-dkh-solution.html)
> (Note: You will need a whole gallon of distilled water to do this.)
> 1. Start with 6 cups of distilled water in a clean measuring container
> 2. Add 1/8 teaspoon Sodium Bicarbonate (baking soda, freshly opened) to the 6 cups of water and mix
> 3. Pour out 3 cups of this mix and discard
> 4. Add back 3 cups of distilled water and mix
> 5. Pour out 3 cups of this mix and discard
> 6. Add back 3 cups of distilled water and mix
> 7. Pour out 1 cup of this mix and discard
> 8. Add back 1 cup of distilled water and mix
> 7. Water comes out to a 4 dKH solution
> 8. To make a 2 dKH solution, mix one cup of the 4 dKH solution with one cup of distilled water.
> 9. To make a 1 dKH solution, mix one cup of the 2 dKH solution with one cup of distilled water.


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## Hoppy

Atmospheric CO2 is enough to make a 4 dKH standard reference solution be dark blue. Adding an acid to lower the pH would only introduce more inaccuracy. The only improvements I know of for drop checkers are:
Use a pH meter instead of the pH reagent.
Improve the time response of the DC by increasing the contact area between the tank water to trapped air, and the trapped air to DC solution, plus reducing the volume of the DC solution.
Both of those improvements are doable if you use a semi-permeable membrane instead of trapped air to separate the tank water from the DC water. But, it isn't an easy design to do, and have it work well.


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## markstr

Thanks Hoppy for that info. I just thought I saw a while back you responded to something in regards to this and mentioned about 2-3 drops of PH solution to add. Probably didn't catch it right LOL .. So, I'll just use the made up 4dkh solution and see what kind of readings I get.
Thank you again ....


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## markstr

Hoppy, here I found it. Does this sound Familiar ?

First buy or make a 4 dKH standard solution (consisting of distilled water and a tiny bit of baking soda only). There are several ways to make it, including http://www.plantedtank.net/forums/fe...tml#post801218

Fill the drop checker bulb about half full of this 4 dKH water, then add 2-3 drops of pH test kit reagent, one that is yellow at low pH and blue at high pH, such as the API pH test kit reagent.


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## Hoppy

Of course you do need to add a pH indicator solution, but you don't add anything to change the pH of the water in the drop checker.


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## AquariumNoob

Someone otta do one of these for Ph! . Bought a PH Pen which needs calibration, and ive got no access to any fancy stuff nor do i want to spend another 15$ On bottles of stuff for calibration.


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## Hoppy

Standard pH solutions are much more difficult and complicated than the "salt" solutions this thread is about. If someone is a good chemist, and can design a kitchen measuring equipment way to make standard pH solutions please do so, and I will put them in the first post in the thread.


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## Mathman

Thank you very much for the instruction on how to make a 4dKh solution. 


I just finished making it and tested the water with a new API KH test...perfect 4 degrees.

Now, I'll add some to my drop checker and stick it inside the tank. Should the color change in a few hours to indicate the level of co2 in the water?


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## Mathman

I think I should have read the previous post...I already had some API Ph test kit...I added 3 drops to the drop checker along with the KH solution and now I have a reading...thanks


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## R. David Jain

*An alternate 4dKH recipe*

Here are some instructions I wrote up for an alternate method to make 4dKH solution. I had two main goals in coming up with this method: The first was to avoid the need for accurate weighing equipment (in fact, there is no weighing at all in this method, just measuring volumes). The second was to have it work even if the baking soda is not "fresh"... so that it would be precise even using an already-opened package that may have absorbed some water. The answer to both these requirements was to start with a fully saturated solution of baking soda and dilute from there. Since the saturation concentrations of sodium bicarbonate in (distilled) water are well-defined and known, this should (and in my estimation DOES) give good results, without having to measure out small amounts of baking soda ("is my level teaspoon level enough? Is the soda too compacted? How do I measure out 2 grams and how much of that is water??"). After some science facts and preliminaries, I lay out the steps below. I didn't have the energy to make a separate "what you will need" section, so you may want to read through the instructions first and make a list (almost everything is something that most people, especially fish-keepers, will have around the house anyway). The steps are simple enough, if long-winded, and this level of precision really isn't necessary probably for most people, but it was fun to come up with, and gives me peace of mind knowing that my "4dKH" solution is accurate to a few percent, and I won't inadvertently gas my fish .

Without further ado...
Relevant solubility figures (in water) for sodium bicarbonate 
(see full temperature range of solubility at: http://www.tatachemicals.com/europe/products/pdf/sodium_bicarbonate/technical_solubility.pdf)
---------------------------
69 g/L (0 °C) 
96 g/L (20 °C) 
165 g/L (60 °C) 
236 g/L (100 °C) 
Solubility vs. temperature is highly linear in the full range 0-100C relevant for liquid water, so one can interpolate 
from these figures as needed. For example, interpolating the solubility at 25C using the data points for 0C and 20C
gives (solubility at 25C) ~ [96 + 5*(96-69)/20]=102.75 g/L, and this is close enough for our purposes. 

Our goal in this process will be to reach a concentration of 120mg/liter NaHCO3. From Wikipedia (edited for brevity): 
"An aqueous solution containing 120 mg NaHCO3 (baking soda) per litre of water will contain 1.4285 mmol/L of bicarbonate.
...Since one degree KH = 17.848 mg/L CaCO3, this solution has a KH of 4.0052 degrees."


Notes:
----------------
"Water" throughout refers to distilled (or de-ionized) water.
Dilution ratios are given as (amount total final mixture) : (amount starting solution). So, "Dilute 2:1" means 
mix 1 part starting solution with 1 part distilled water.

"1 Cup" here does not necessarily have to mean 1 8oz cup (though it could be). You can decide on exactly what size 
"cup" you would like to use depending on your needs. Larger quantities mean a more accurate dilution, but more wasted
materials (baking soda and distilled water). I chose to use a "cup" size which was actually 3/4cup=180mL because I had
a 3/4 measuring cup handy. 

Be sure to wash and thoroughly dry (tap water is fine for this) your mixing vessels at EACH STAGE of the dilution. 
Because we will be diluting over several orders of magnitude in concentration, even a small residue of higher 
concentration material from an earlier step (say, from re-using the mixing vessels) will throw off the final 
concentration. 

Steps
-----------------
1) Create a saturated solution of sodium bicarbonate. First mix 2cups hot water with enough baking soda to saturate the solution. You will know that it's saturated when no more of the powder can dissolve and any additional amount added falls to the bottom of your mixing vessel. Using hot water (distilled water heated on the stove) ensures that the solution is truly saturated. After dissolving, we will cool the water back to room temperature, allowing any excess to precipitate out. Do not heat the water too much (warm to the touch is fine)!! At high temperatures, the bicarbonate ions begin releasing C02 and water to form carbonate ions, which will throw off the calculations.

2) Cool the water back to room temperature. For me, this was 25C, so my calculations in the later steps are based on this number. Adjust your numbers accordingly. Using an electronic temperature probe (like one used for cooking) submerged directly in the water will help you tell when the temperature has finished dropping and give you a more precise final temperature reading than a wall thermometer or home thermostat.

3) Do an initial dilution of 2:1. I would suggest bottling and saving a large portion (1cup or more) of this initial dilution to use for making more 4dKH water in the future, without having to repeat steps 1 and 2). You probably want to use a coffee filter for this initial dilution to get out any precipitated bits of baking soda. By diluting 2:1, we ensure no further precipitation of the bicarbonate out of solution, even if the temperature drops. Be sure to label the concentration of this solution on the bottle based on your temperature reading and the 2:1 dilution!!

4) Assuming the temperature of your starting solution was 25C, after this 2:1 dilution, you will have a concentration of 51.375 g/L (one half the saturation concentration read-off or interpolated from the solubility information above, based on your solution's temperature after cooling). Let's get diluting! We need to dilute by an overall factor of [51375mg/L]/[120mg/L]=428.125 (adjust the first number on the left as needed).

5) Dilute in a ratio of 2:1 8 times (NOT counting the initial 2:1 dilution). Keep track of your dilutions!! I STRONGLY suggest you have a pad of paper next to you to check off each 2:1 dilution, to make sure you do exactly 8). After this, the solution will be at 6.69 dKH (=428.125/2^8*4dKH if the starting solution was at 25C... adjust this number according to your situation).

6) The final step requires some precision in terms of measuring volumes, but if you have a dropper that can measure 1mL, an API test kit with test tubes marked with a 5mL line, and a larger measuring cup that can measure a few hundred mL's at a time in increments of 10 (available in most bigger supermarkets' cooking sections), it shouldn't be too hard. We need 
to take the 6.69dKH solution that we now have (or whatever you got based on your starting temperature) and dilute it down to 4dKH. In the following formula, replace 6.69 with whatever your number is. Defining x as the number of mL's of distilled water that we need to add, and Y as the number of mL's in your user-defined "cup" (you should have at this point exactly 2 "cups" of diluted fluid), with some simple reasoning we can derive the equation:
x= 2Y*(6.69/4 - 1)
Once you add this many mL of water to the 2 "cups" of solution you already have, the resulting mixture will be at 4dKH! We're done!! Now bottle that sh*t! (Small refillable bottles for toiletries or what have you can be bought at a well-stocked grocery or drug store).

7) Testing: When I tested my results with the standard API KH tester, it changed color at 6 drops (indicating a KH of between 5 and 6 degrees). You will probably get a similar "off" result. Do not worry! These tests are notoriously imprecise (or rather, they are precise enough for the needs of typical aquarists, but they are not lab quality). I got independent confirmation of this fact when I had my local fish store test a sample of water that I had just tested for comparison. Their result was 2.1dKH, while mine was 4dKH (to within the error implied by counting a discrete number of drops). I don't know for sure what method they were using, but it was likely more accurate than mine (based on the fact that they can afford, and have interest in owning, more accurate equipment, coupled with the fact that they quoted me a number to the first decimal place, whereas your standard kit "rounds" to the nearest whole number). So, this tells me that my kit probably tests a little high, meaning that my reading of 5-6 was really closer to the 4 we should expect. In the end, the real "proof" of this method is in the procedure. So long as we followed the steps correctly (and that basic science works), there should be no reason not to get the 4dKH solution we were expecting. Still and all, a "sanity" check at the end is useful, just to reassure ourselves that we didn't screw something up TOO badly . If your number is way different from 4, then you might have mis-counted dilutions, have an expired test kit, or run into some other unknown gremlin. Short of this, just go ahead and assume that the solution is what it should be.

Happy drop-checking! I hope some of you out there find this useful .


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## Beer

This thread has been linked to recently and there were requests for pH calibration.

This link gives a description of a high range calibration solution using 1/2 tsp of borax to a pint of water at a known temperature. Somewhere around room temperature should be sufficient enough for the accuracy of these kits. There is also a link in the article for lower pH solutions.


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## manlyfan76

What kit do ppl think is best for Nitrates? or should we use any kit with the help of the calibration?


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## Darkblade48

manlyfan76 said:


> What kit do ppl think is best for Nitrates? or should we use any kit with the help of the calibration?


For general purposes, the API and Sera test kits seem to be reasonably reliable.

The most accurate ones I have used are made by LaMotte, but they are pricy.

Of course, with any test kit, once calibrated, you can expect a reasonable degree of precision. With more expensive test kits, you will get both precision and accuracy.


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## manlyfan76

Darkblade48 said:


> For general purposes, the API and Sera test kits seem to be reasonably reliable.
> 
> The most accurate ones I have used are made by LaMotte, but they are pricy.
> 
> Of course, with any test kit, once calibrated, you can expect a reasonable degree of precision. With more expensive test kits, you will get both precision and accuracy.


I use Lamotte test kits at work ( swimming pool shop) I may check them out.


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## rick dale

*test sample longevity*

How long will the calibrated test samples stay true ? Do they need to be stored at a certain temp , or does it matter ?


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## Hoppy

If the test sample is made up of inorganic chemicals and water, you can store them indefinitely, as long as none of the water evaporates. That can be hard to do.


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## Malakian

Hoppy said:


> If the test sample is made up of inorganic chemicals and water, you can store them indefinitely, as long as none of the water evaporates. That can be hard to do.


For clarification, would most test be inorganic or does it depend on brand/test?


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## jrill

Malakian said:


> For clarification, would most test be inorganic or does it depend on brand/test?


 He's referring to the sample here not the test kit.


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## Malakian

yes, that was what I meant. So to ask in another way, can you make calibrated solution for all tests/brands and store them indefinitely? Or is it test/brand (chemicals used for the tests) dependent? As in some test/brand use organic chemicals?

Bump: nevermind, think I got it know. You mean you can store the, say 25ppm,50ppm NO3 made up solutions, then add new test reagent to both calibrated water and tank water, as in you have to first do the calibrated solution test every time to get a reference for the tank test? I thought you meant you could mix it up to show the color, then store it? Sorry, I am a bit confused now..


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## Hoppy

You can't mix a known sample of nitrate in water, for example, then add the test reagent to get the color, then save that colored sample to refer back to later. The color comes from dyes in the reagents, and dyes are not stable chemicals. You might be able to store them for a week or so, but definitely not for years.


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## Malakian

Big misunderstanding from my part, been a lot of that lately. Thanks for clearing it up for a brick headed viking


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## keymastr

Any way to calibrate a GH test? My API tests are impossible to read. The color gets just slightly darker green/green yellow with each drop but does not ever make the dramatic change that I have seen of other peoples tests. I guess it may have been a bad kit.


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## Hoppy

My experience is that GH test kits have a very limited shelf life before they just stop changing color when you try to use them. There is no reason I'm aware of to measure GH with much accuracy, so even a poor test kit, that is off 20% on the readings, is adequate. For that reason I don't think it is worth the trouble to figure out a good easy way to calibrate a GH test kit, but I'm sure it can be done.


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## aclaar877

Hoppy said:


> My experience is that GH test kits have a very limited shelf life before they just stop changing color when you try to use them. There is no reason I'm aware of to measure GH with much accuracy, so even a poor test kit, that is off 20% on the readings, is adequate. For that reason I don't think it is worth the trouble to figure out a good easy way to calibrate a GH test kit, but I'm sure it can be done.


Agree - I have an 10 year-old API GH test kit and it does the same thing - it never shows the definite color change. You could ask around locally to see what the tap GH is - maybe LFS has a test kit and could run a test for you as well.


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## mistergreen

You can skip GH and buy a cheap digital TDS meter ($10). TDS is a good way to test water softness/hardness.

You can make a simple NaCl (table salt) calibration solution. 1mg/L is 1ppm. And there's about 5690 mg in a teaspoon. A meter only goes up to 1000ppm so you'll have to dilute the solution.


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## ChuckM

A question on behalf of us AquaDummies:
KNO3 = SaltPeter? Or where would one find this?

I have two API test kits whose nitrate tests report very different results on the same sample. One, less than a year old, reports upward to 160 ppm while the other reports 20ppm.


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## jeffkrol

ChuckM said:


> A question on behalf of us AquaDummies:
> KNO3 = SaltPeter? Or where would one find this?
> 
> I have two API test kits whose nitrate tests report very different results on the same sample. One, less than a year old, reports upward to 160 ppm while the other reports 20ppm.


first:
https://www.walmart.com/ip/Potassium-Nitrate-Powder-KNO3-1-2-Lb/730344998


Could give you the standard answer that the second reagent really isn't a solution but a suspension. If not properly beat to bejesus it will be inaccurate..
One possibility is it was accidentally used up prev in big cloudy clumps..


.

Switched to Seifert personally..


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## ChuckM

jeffkrol said:


> first:
> https://www.walmart.com/ip/Potassium-Nitrate-Powder-KNO3-1-2-Lb/730344998
> 
> 
> Could give you the standard answer that the second reagent really isn't a solution but a suspension. If not properly beat to bejesus it will be inaccurate..
> One possibility is it was accidentally used up prev in big cloudy clumps..
> 
> 
> .
> 
> Switched to Seifert personally..



Yeah, I followed protocol and 'shook vigorously' for a full 30 seconds, always do. Maybe I'll try beating it too.
One other thing I noticed was the two vials side-by-side didn't have exactly the same amount of liquids. I actually redid the test thinking I miscounted the number of drops but the one showing lower ppm had, at most, 1/16" less liquid. Samples are equal poured till the bottom of the miniscus reaches the line.


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## Greggz

jeffkrol said:


> Switched to Seifert personally..


+1.

I use reference solutions to do a side by side test with Salifert and API test kits and posted it in my journal.

https://www.plantedtank.net/forums/12-tank-journals/1020497-greggz-120g-rainbow-fish-tank-camera-pro-mode-settings-8-12-2018-a-56.html.

Even a new API test was not very accurate. And like mentioned, if you don't pound the heck out of it EVERY time, then it's worse.

The Salifert kit was spot on.

So just saying I would take whatever reading you get with the API as a VERY rough estimate, and wouldn't base too many decisions around it.


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## PlantedRich

I think what happens and what Jeff was hinting at is that the chemicals in one test bottle may no longer be what they should. When new and we fail to shake them well enough, which is a pretty common thing apparently, we get too much of one component used out of that bottle and each time we do a test, we use more of that portion until there is no way we will get the correct answer even when beating it to death. My thinking, for simple, is that the one bottle is more than one item until we mix them well. So if we use that bottle, we get too much used of one of those items and then when we get into shaking it really well, we have missed the prime /correct mix in that bottle. 
For example, if we added salt to water and did not mix it well to dissolve the salt, we might turn the bottle over, use the salt out and not really ever get the true salt water mix we wanted? So then we try really, really, mixing but much of the salt is already gone from the prior uses? 
Shake them well? I even made a shaker for a reciprocating saw and never got the good answers! I gave up on a test that was that difficult to use and also went to the Salifert brand test kit to get good results. I can see the pink much better and I am willing to pay the extra to get a usable/reliable answer versus a cheap but unreliable test report.


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## ChuckM

PlantedRich said:


> I think what happens and what Jeff was hinting at is that the chemicals in one test bottle may no longer be what they should. When new and we fail to shake them well enough, which is a pretty common thing apparently, we get too much of one component used out of that bottle and each time we do a test, we use more of that portion until there is no way we will get the correct answer even when beating it to death. My thinking, for simple, is that the one bottle is more than one item until we mix them well. So if we use that bottle, we get too much used of one of those items and then when we get into shaking it really well, we have missed the prime /correct mix in that bottle.
> For example, if we added salt to water and did not mix it well to dissolve the salt, we might turn the bottle over, use the salt out and not really ever get the true salt water mix we wanted? So then we try really, really, mixing but much of the salt is already gone from the prior uses?
> Shake them well? I even made a shaker for a reciprocating saw and never got the good answers! I gave up on a test that was that difficult to use and also went to the Salifert brand test kit to get good results. I can see the pink much better and I am willing to pay the extra to get a usable/reliable answer versus a cheap but unreliable test report.



Yep, I get all that and everything else posted. Thanks!
I have both a pound of KNO3 and a Salifert test on order now.


I'm kind of returning to the hobby, and for the first time have become concerned about water testing. Never seemed to be an issue in previous planted tanks; water was always clear, fish happy, plants grew. But now in Aquarium Hobby v.2.0 I'm experimenting with anoxic filtration using Safe T Sorb as a substrate and plenums in a 65 gallon and a Fluval Edge 6 gal. (it was a freebie) so these metrics are more critical. 4 months into it I'm finding (according to API): pH 7.6-7.8, Ammonia 25 -50 ppm, Nitrates 0 and Nitrates 80 - 160. Fish seem happy, plants look healthy (who wants some Hornwort?). Algae was a bit of a problem in the Edge but breaking up the lighting period into two parts with a 2 hour break seemed to being that into check. No CO2 being added.


But before I do anything else I need to know what's happening with the water.
Thanks for the valuable feedback. Wish I'd known about the API issues 4 months ago!


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## PlantedRich

Big , yes on the wish we had known! It's a trek!


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## Jezza

Calibrating Test Kits - for non-Chemists
API NO3 Test Kit

Thought I’d post my results for the heck of it ☺

All testing as per API NO3 Test Kit Instructions.
API Test Bottle #2 shaken for 1 min before each test.
All photos on the LHS are taken with the test vial flat against the card.
All photos on the RHS are taken spaced off the card by my index finger (approx 1/2”)
Lighting: Chihiros A II Series A451 @50% Intensity (1950lm 21w 8500K)
Camera: iPhone XR (No filters or aperture adjustment)
API NO3 Calibration Test for 800 ppm nitrate standard water.

TDS: 670ppm
Reading API NO3 Card @ Test Station: N/A - No test taken 
Test 1.
API NO3 Calibration Test for 100 ppm nitrate standard water.

TDS: 90ppm
Reading API NO3 Card @ Test Station: 80ppm








Test 2.
API NO3 Calibration Test for 50 ppm nitrate standard water.

TDS: 45ppm
Reading API NO3 Card @ Test Station: 40ppm








Test 3.
API NO3 Calibration Test for 25 ppm nitrate standard water.

TDS: 23ppm
Reading API NO3 Card @ Test Station: 30ppm








Test 4.
API NO3 Calibration Test for 10 ppm nitrate standard water.

TDS: 9ppm
Reading API NO3 Card @ Test Station: 10ppm








Test 5. 
API NO3 Calibration Test for 5 ppm nitrate standard water.

TDS: 2ppm
Reading API NO3 Card @ Test Station: 0-5ppm








Test 6.
API NO3 Calibration Test for Distilled Water:

TDS: 0ppm
Reading API NO3 Card @ Test Station: 0ppm


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