# TDS meter?



## Maryland Guppy (Dec 6, 2014)

Evilbay usually has a 2 pen set pH/TDS with 7.0 calibration fluid for under $20 with free shipping.
For hobby level testing this should be fine.


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## bsherwood (Nov 22, 2007)

I will check it out! thank you
b


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## dukydaf (Dec 27, 2004)

bsherwood said:


> OK, I am not a fan of the chemistry
> 
> is there a better TDS Meter.


Hey you will be glad to hear a TDS Meter has more to do with physics than with chemistry:grin2:, as it actually measures conductivity of the solution. 

As for a better... they are pretty basic instruments and in my opinion in planted aquariums you do not a supper accurate one. This is because the TDS value is already a sum value of many things disolved in the water (so already has a large error). So don't spend hundreds on one .

As long as it is relatively precise ( ie you can compare the values from the same instrument) it will do the job.

Enjoy the chemistry of the planted tank.


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## Edward (Apr 11, 2005)

Hi bsherwood
You will find maintaining water quality to be easier and faster with a TDS tester than with test kits. It may not tell the whole story in details but it will include what test kits can’t. Once you get to know the routine you won’t need any of the test kits. 
They are $5 on eBay, any will do. Just make sure it reads in µS units. There are other units for different applications.


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## bsherwood (Nov 22, 2007)

Thank you Edward!!!

Thankyou to everyone....we are so fortunate to have this forum as a resource for our passion.


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## hidden.inverts (Feb 28, 2016)

I just received this pH, TDS, & Temp pen I bought from eBay, yesterday.
3 in 1 Pen Type Waterproof LCD Digital Ph TDS Temp Meter:








So far I really like it, it makes things a lot easier and seems to be accurate.
I haven't had a chance to calibrate it yet as I have yet to receive my calibration solutions, but calibration seems easy enough.
Comparing results with my API test kits, it seems to be accurate as far as pH and temperature.
I like this pen more because it has both pH and TDS, the others I've seen are either only pH or TDS, but not both.
It cost about $23.00 on eBay, but I also had to spend about the same buying 4 button batteries at Target.


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## bsherwood (Nov 22, 2007)

TDS meter has been shipped! should have it in a few days.
thanks for all the advice folks!


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## 9thdragon (May 9, 2015)

hidden.inverts said:


> I just received this pH, TDS, & Temp pen I bought from eBay, yesterday.
> 3 in 1 Pen Type Waterproof LCD Digital Ph TDS Temp Meter:
> 
> 
> ...




I don't see it says package included in the meter stick
I want one >.<


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## bsherwood (Nov 22, 2007)

Meter has arrived.....testing all tanks....my shrimp tanks??? TDS over 600!!!!!!!!! I had read that you need not do water changes on a shrimp tank as long as you are keeping nitrates, amonia, nitrite in check.....but holy smokes!!! my other planted tanks , where I do regular changes was much much lower.....

I have been doing partial changes on the shrimp tanks the past 2-3 days....tds is below 400 but "discobee" says to keep tds in the 100-180 range???

out of the tap I am at 185 in TDS



three years ago I gave away my entire RO system to my nephew. I was getting out of "saltwater aquariums" and would never need an RO unit again.....
yes, I am a moron


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## Edward (Apr 11, 2005)

bsherwood said:


> … out of the tap I am at 185 in TDS …


 Excellent,
though one question,
TDS at 185 of what, gallon, inch? There is more than one TDS unit.


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## bsherwood (Nov 22, 2007)

I suppose it was about a quart of tap water....


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## Edward (Apr 11, 2005)

bsherwood said:


> I suppose it was about a quart of tap water....


The amount of water makes no difference. What I am referring to is a TDS measurement unit, it can be in ppm, µS, EC, … , if we don’t have this information, we don’t know what the actual TDS is.


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## bsherwood (Nov 22, 2007)

DOH!

ppm


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## Edward (Apr 11, 2005)

bsherwood said:


> ppm


 TDS in ppm is for kitchen salt applications, not for aquariums. Aquariums use µS because of the solids involved. 
You can switch the TDS meter to µS reading and get a different value.


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## bsherwood (Nov 22, 2007)

there must be a conversion chart?? no?

Bump: This is the meter


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## Edward (Apr 11, 2005)

How do I convert ppm TDS to µS TDS?
The conversion rate is not linear, only estimated and dependent on the actual TDS meter mode.

TDS meter mode:
NaCl -> 1.47 to 1.50
442 -> 1.65 to 1.85
KCl -> 1.50 to 1.57

µS TDS ≈ ppm TDS * 1.50 (for NaCl mode)

Example
150 µS TDS ≈ 100 ppm TDS * 1.50

Please see post #25 below, thank you.


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## Pattern8 (Dec 9, 2015)

Edward said:


> TDS in ppm is for kitchen salt applications, not for aquariums. Aquariums use µS because of the solids involved.
> You can switch the TDS meter to µS reading and get a different value.


I think I'm a little confused about this unit measurement conversion as well. I don't think my device has the option to display anything other than ppm. So when reading other posts on TDS readings are most people using ppm or the other (I can't find the character in my keyboard)?


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## Edward (Apr 11, 2005)

Pattern8 said:


> I think I'm a little confused about this unit measurement conversion as well. I don't think my device has the option to display anything other than ppm. So when reading other posts on TDS readings are most people using ppm or the other (I can't find the character in my keyboard)?


Text and posts mentioning TDS without a unit (ppm, µS, EC,) have no merits. 

To type “µ”, hold Alt + 230, or type microS.


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## hidden.inverts (Feb 28, 2016)

My TDS for my planted community tank with Amano and RCS is currently at 230ppm.
When I first got my pen it was at around 400ppm.. I did a small 10% water change with RO water with a TDS of 20 and it went down to 220ish..
All livestock and plants are doing fine at this TDS level.. RCS are molting and 3 are currently berried.. We'll see how the babies do in 20ish days..
My TDS pen also measures in x10 ppm.. not sure in which mode NaCl, 442, or KCl.
What do these Chinese TDS pens typically use?

Also, I suggest purchasing calibration solutions for TDS 1000ppm and 1500ppm or something and making sure it's calibrated.
Mine was off by about +50ppm TDS out of the box.
This is what I picked up, since my pen also measures pH.


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## Edward (Apr 11, 2005)

hidden.inverts said:


> … When I first got my pen it was at around 400ppm.. I did a small 10% water change with RO water with a TDS of 20 and it went down to 220ish..


 One 10% water change with RO water at 20 will change aquarium water from 400 to 360, not 220. Something is not right.



> My TDS pen also measures in x10 ppm.. not sure in which mode NaCl, 442, or KCl.
> What do these Chinese TDS pens typically use?
> Also, I suggest purchasing calibration solutions for TDS 1000ppm and 1500ppm or something and making sure it's calibrated.
> Mine was off by about +50ppm TDS out of the box.


 How do you calibrate an unknown mode meter with unknown calibration solution? 

One easy way to check a TDS meter is to test city water tap. Read utility water report what the value is and compare it with your reading.


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## hidden.inverts (Feb 28, 2016)

Edward said:


> One 10% water change with RO water at 20 will change aquarium water from 400 to 360, not 220. Something is not right.
> 
> How do you calibrate an unknown mode meter with unknown calibration solution?
> 
> One easy way to check a TDS meter is to test city water tap. Read utility water report what the value is and compare it with your reading.


I don't know about calibrating unknown mode meter with unknown calibration solution as I didn't know there were different ways TDS could be measured. I initially had thought all the pens measured in the same standard of measurement ppm.

When I bought my other 1000ppm TDS calibration solution to have 2 points to calibrate to it stated: "Any brand TDS meter can be calibrated to any brand of calibration solution"
http://amzn.com/B001FD6WZ8

Wouldn't measuring what comes out of my tap differ from what the water company tests results are? I would imagine it would have to go through pipes picking up more TDS along the way?


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## Edward (Apr 11, 2005)

People are ordering TDS meters in ppm instead of µS micro Siemens. If you already have one in ppm then you can still use it. 

Read aquarium ppm and read tap ppm. 
If the aquarium ppm = tap ppm + 100, then water change is due.

Please see post #25 below, thank you.


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## jw.cS (Jan 13, 2005)

Hi bsherwood. *waves enthusiastically*

I recently got this TDS meter that gives the results in microSiemens (µS).

Amazon.com: HM Digital AP-2 AquaPro Water Quality Electrical Conductivity Tester, 0-9999 µS Range, 1 µS Resolution, +/- 2% Readout Accuracy: Home Improvement


It's pricier than the $5/$10 ones that you usually see referenced but, for the life of me, I can't find one in that price range. Everything in that price range gives the results in ppm of some salt; and, as Edward has pointed out, you can't accurately convert ppm to µS because the conversion rate isn't linear and it is dependent on whatever salt your meter was calibrated at. :icon_roll Maybe I just suck at searching. *shrugs* 

---

Side note: From various readings and youtube videos, I am beginning to think most TDS numbers that you find referenced is in ppm of the author's meter instead of in µS...but that's a story for another day.


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## Edward (Apr 11, 2005)

> How do I convert ppm TDS to µS TDS?
> The conversion rate is not linear, only estimated and dependent on the actual TDS meter mode.
> 
> TDS meter mode:
> ...





> People are ordering TDS meters in ppm instead of µS micro Siemens. If you already have the one in ppm then you can still use it.
> 
> Read aquarium ppm and read tap ppm.
> If the aquarium ppm = tap ppm + 100, then water change is due.


While looking at the conversion modes above, I have decided to test one TDS ppm meter against a TDS µS meter. The results are,

Both meters are perfectly linear, straight line from 0 to 40 ppm with macros fertilizer referenced to NO3 and resolution of 2 ppm. This means that both, µS and ppm TDS meters are suitable for aquariums.

The less than good news is the ppm TDS meter’s numbers. We know there are three TDS modes, NaCl, 442 and KCl. The one I tested reads 2.65 times lower than the µS meter, far from the 1.47 – 1.85. I hope this is due to calibration. 

This is why I would like to ask you all to take a reading and post the result here. 
We need to know the reading of 1L of water with no fertilizer and with fertilizer. The fertilizer is 10 drops of PPS-Pro solution #1 macros in 1L. (Referenced to 20 ppm of NO3)

These numbers are the real values to determine your water changes. (100 applies only to µS)

Thank you.


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## Edward (Apr 11, 2005)

There is a variety of TDS meter modes and units, KCl ppm, “442” ppm, NaCl ppm, µS microS and converting between them is impractical. In order to overcome this we can use the following,

Take three readings,
tap
tap with 10 drops of solution #1 macros in 1000 ml
aquarium

then,
water change IF [ aquarium ] > [ tap with 10 drops of solution #1 macros in 1000 ml ]

The first two readings will not change, so only one reading will be needed to determine water changes. The aquarium readings.


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## Bobbybills (Nov 30, 2015)

Edward said:


> While looking at the conversion modes above, I have decided to test one TDS ppm meter against a TDS µS meter. The results are,
> 
> Both meters are perfectly linear, straight line from 0 to 40 ppm with macros fertilizer referenced to NO3 and resolution of 2 ppm. This means that both, µS and ppm TDS meters are suitable for aquariums.
> 
> ...


Last 6 readings each day using TDS-4 in NaCl ppm and AP-2 in µS, both by HM Digital. 

PPM µS Conversion factor 

159	294	1.849
143	266	1.860
148	276	1.865
151	281	1.861
153	287	1.876
163	306	1.877

Hope this helps


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## Immortal1 (Feb 18, 2015)

Just received my TDS meter today and did some various testing. Results as follows;

Distilled water = EC 28 µs/cm (73 f)
Tap water sitting in sump for 24 hours = EC 394 µs/cm (76.5 f)
20g tank = EC 566 µs/cm (76.1 f)
40g tank = EC 488 µs/cm (76.9 f)
75g tank = EC 464 µs/cm (77.4 f)

Tap = 7dKH, 12dGH, degassed pH of 7.6

Using the above information (best I can tell) I should do a water change on the 20g and I am getting close to a water change on the 40g.
Thoughts?


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## Oso Polar (Apr 22, 2015)

TDS meter should report results in ppm not in µS/cm, if it is in µS/cm then it is an electrical conductivity meter (EC meter). TDS is estimated from EC but conversion factor depends on the temperature, so good meters also measure temperature and apply temperature compensation automatically.

EC 28 µs/cm is anything but distilled water. Or your meter shows some random numbers. :grin2: Should be zero. May be one. Okay, may be two.


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## Immortal1 (Feb 18, 2015)

For what it's worth, the meter I have "has an automatic temperature compensation function (using 3 temperature coefficients) when measuring solutions". And no, I don't know precisely what that means .
I can switch it over to TDS 0-9990 ppm and see what kind of readings I get.

Distilled Water = TDS 3ppm (75 f)
Sump Water = TDS 198 ppm (76 f)
20g = TDS 286 ppm (76 f)
40g = TDS 242 ppm (77 f)
75g = TDS 233 ppm (77 f)


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## Edward (Apr 11, 2005)

Actually TDS as total dissolved solids measurement in µS micro Siemens is the real electrical conductivity measurement. Anything else is only an artificial conversion to fit some specific salt ppm agenda. 

RO filter rejection ratio is usually about 90% which means tap is stripped of 90% of solids. The remaining 10% remains. Let’s say tap is 394 µS then RO at 90% rejection should produce 39 µS output. RO product water can never be zero.


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## Oso Polar (Apr 22, 2015)

Nope, this is wrong. TDS is measured in ppm (or mg/L), it is *never* measured as conductivity. This is not conductivity, this is a measure of dissolved solids in water. The real way to measure TDS is to evaporate water and then weight the solid residue. As this is too time consuming these portable TDS meters they really measure conductivity and then *estimate* TDS assuming certain salt composition dissolved in the water and adjusting conductivity measurements by temperature.

See here: Knowledge Base - Hanna Instruments

Good RO rejection rate is > 98 percent, still I never saw distilled water with TDS bigger than my RO water (TDS 6). Well, I only saw 0 and 1.


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## Immortal1 (Feb 18, 2015)

bsherwood said:


> Meter has arrived.....testing all tanks....my shrimp tanks??? TDS over 600!!!!!!!!! I had read that you need not do water changes on a shrimp tank as long as you are keeping nitrates, amonia, nitrite in check.....but holy smokes!!! my other planted tanks , where I do regular changes was much much lower.....
> 
> I have been doing partial changes on the shrimp tanks the past 2-3 days....tds is below 400 but "discobee" says to keep tds in the 100-180 range???
> 
> out of the tap I am at 185 in TDS


Curious, seeing as you are also from the upper midwest and your tap runs TDS 185 ppm, I am curios what your GH, KH, and pH are like. 
My area measures 12 GH, 7 KH, and 7.6 pH and TDS out of the tap is 198 ppm.


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## mistergreen (Dec 9, 2006)

All sensors need to be calibrated for accuracy. Read the instructions. Salt water is used at a specific ppm.

These digital sensors output in ppm usually unless the manual says otherwise.
The conductivity readings are temperature dependent when converted to ppm. So it's best to buy a sensor with a thermometer built in.

500+ppm TDS in water is considered by the EPA as contaminated water


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## Immortal1 (Feb 18, 2015)

Good bit of info mistergreen regarding the 500+ ppm. Fortunately, none of my tanks are considered "contaminated". But, I would be curious what the Mississippi River water shows on the TDS.


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## Edward (Apr 11, 2005)

https://www.youtube.com/watch?v=MTAbuTYGk0M&nohtml5=False


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## mistergreen (Dec 9, 2006)

Edward said:


> https://www.youtube.com/watch?v=MTAbuTYGk0M&nohtml5=False


Amazon.com: Etekcity Digital Handheld TDS Meter , +/- 2% High Accuracy, 0-9990 ppm (Blue): Home Improvement


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## Edward (Apr 11, 2005)

“_TDS meters usually read in ppm unless the manual says otherwise._ “

That’s nice, but there is more than one TDS ppm system (KCl, 442, NaCl) plus manufacturer variations. They don’t read the same values.

Though, there is only one TDS in µS micro Siemens.


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## mistergreen (Dec 9, 2006)

Edward said:


> “_TDS meters usually read in ppm unless the manual says otherwise._ “
> 
> That’s nice, but there is more than one TDS ppm system (KCl, 442, NaCl) plus manufacturer variations. They don’t read the same values.
> 
> Though, there is only one TDS in µS micro Siemens.


microsiemens and tds are not the same thing.

TDS Meters, Conductivity and Conversion Factors - HM Digital


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## Edward (Apr 11, 2005)

TDS meters in ppm are perfect tools for fast assessment of ppm or mg/L of specific single salt solutions. 

Aquarium water is not distilled water with kitchen salt only or with potassium chloride only. Aquarium water contains dozens of dissolved elements. Every element has a different impact on readings. Using a single salt reading device on complex aquarium water is producing misleading results.
...


I have tested couple of compounds with a Cole-Parmer µS meter and calculated ppm as NaCl. Tested chemicals are 300 ppm or mg/L in RO water, values are as net increase. 

ppm as NaCl, µS, compound

2, 4, CO(NH2)2 Urea
115, 235, CaSO4.2H2O
120, 246, KH2PO4
133, 273, MgSO4.7H2O
153, 314, NaHCO3 baking soda
180, 368, Ca(NO3)2.4H2O
220, 450, KNO3
221, 452, CaCl2.2H2O
253, 518, K2SO4
280, 573, NH4NO3
300, 614, NaCl salt pickling
300, 614, NaCl salt iodized
300, 614, sea salt

If interested in sharing results, 
Dissolve 3.0 g in 1000 ml RO
Take 100 ml
Add 900 ml RO to the 100 ml
Take chemical reading
Value = chemical reading – RO reading


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## Pattern8 (Dec 9, 2015)

You guys have completely lost me but for the sake of sharing I did my own "test"

Started with 5 gallon of RODI water with a TDS of 0ppm
Added 1tsp Seachem Equilibrium, 1050mg Alkaline Buffer, and 972mg Acid Buffer which achieved 6.8 pH, 3° KH, 4° GH
Then added following Seachem Products:
1.2ml Flourish Trace
1.2ml Flourish Nitrogen
2.1ml Flourish Phosporus 
.5ml Prime
1.2ml Fresh Trace 

Which resulted in a TDS of 213ppm


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## Sulla (Dec 31, 2014)

Not to hijack this thread, but I've never owned one of these meters. Is there a brand or model of choice for a pH, TDS, hardness meter?


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## Edward (Apr 11, 2005)

mistergreen
in post #41 Pattern8 is sharing his test results with us. I would like to duplicate it. 

Most posts I have seen would say TDS 213. Pattern8 specifies “ppm”. Thanks to this extra information I can tell that the measurement represents some kind of an equivalent. But it doesn’t say which one. 
TDS 213 ppm as NaCl
TDS 213 ppm as 442
TDS 213 ppm as KCl

I am not sure people even know what equivalent system they use. Please help me understand. Do I automatically assume his measurement is an NaCl equivalent?


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## mistergreen (Dec 9, 2006)

Sulla said:


> Not to hijack this thread, but I've never owned one of these meters. Is there a brand or model of choice for a pH, TDS, hardness meter?


They're pretty much the same except some are temperature compensated. Look for the meters..


Sent from my iPad using Tapatalk HD


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## mistergreen (Dec 9, 2006)

Edward said:


> mistergreen
> in post #41 Pattern8 is sharing his test results with us. I would like to duplicate it.
> 
> Most posts I have seen would say TDS 213. Pattern8 specifies “ppm”. Thanks to this extra information I can tell that the measurement represents some kind of an equivalent. But it doesn’t say which one.
> ...


Yes, these pen meters are NaCl equivalent. The calibration liquid is salt.


Sent from my iPad using Tapatalk HD


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## Sulla (Dec 31, 2014)

Look for the meters?



mistergreen said:


> They're pretty much the same except some are temperature compensated. Look for the meters..
> 
> 
> Sent from my iPad using Tapatalk HD


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## mistergreen (Dec 9, 2006)

Sulla said:


> Look for the meters?


hmmm, my post got edited or chopped off for some reason.
Look for ones that are temperature compensated, ATC (Automatic Temperature Compensation). And the lower the resolution the more accurate like 1%.


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## Edward (Apr 11, 2005)

Immortal1 said:


> Yes, happy to help. My digital scale is accurate to 0.1g
> I do not have RO water, but I know the local fish store sells it for all the marine tanks.
> 
> FYI;
> ...


Thank you for the info. 
Can you please read ppm and µS of 300mg/L (ppm) kitchen salt in RO?

Read RO
Dissolve 30.0 grams of kitchen salt in 1000 ml RO
Take 100 ml
Add 900 ml RO into the 100 ml
Take 100 ml
Add 900 ml RO into the 100 ml
Read salt solution

Liquid, ppm, µS
RO, ?, ?
Salt, ?, ?
Increase, ?, ?

Thank you!


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## Immortal1 (Feb 18, 2015)

I can do that. Unfortunately it will have to wait until Monday. LFS is closed now.


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## Bobbybills (Nov 30, 2015)

My son borrowed the PPM unit to check his RO membrane but I can do the µs reading, or do you need both? Are you trying to confirm the conversion for EC and PPM meters that are calibrated to NaCl? Does it matter if the salt is iodized?


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## Edward (Apr 11, 2005)

Bobbybills said:


> My son borrowed the PPM unit to check his RO membrane but I can do the µs reading, or do you need both? Are you trying to confirm the conversion for EC and PPM meters that are calibrated to NaCl? Does it matter if the salt is iodized?


 Better do both. I am trying to find some sense into so many models so we can use numbers we can share. Also, I am not sure my meters are correct. With salt we can get some connecting numbers I hope and take it from there.

The type of salt should not matter much. I have measured three types and all read the same value. It was kitchen iodized salt, kitchen pickling salt and sea salt.


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## Bobbybills (Nov 30, 2015)

@Edward
Ok, I will get it back next week and do the tests. But can I ask why all the dilution. Why not just start out with .3 grams in 1000ml?


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## Edward (Apr 11, 2005)

Bobbybills said:


> @Edward
> Ok, I will get it back next week and do the tests. But can I ask why all the dilution. Why not just start out with .3 grams in 1000ml?


 It is a matter of accuracy. 

If you have a scale with 0.00 g then you can do 0.30 g theoretically, but the accuracy will suffer. Better to do 3.00 and divide by 10.

For scales with 0.0 g, 30 g and then divide by 10 and 10 to get 300 mg.

And for scales with 1 gram, well, impossible unless we go for 10L and start dividing from there.


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## Oso Polar (Apr 22, 2015)

My RO water has TDS 6. To one liter of water I've added 0.3 g of kitchen iodized salt - got 329 ppm, so salt itself added 323 ppm. Note that one liter of water was measured with a kitchen pitcher whose accuracy is far from ideal. So it is calibrated to NaCl - I believe it should have been exactly 300 ppm (306 accounting for impure RO) if my salt and, especially, water quantity measurements have been better. This is HM Digital TDS-3 (Amazon.com: HM Digital TDS-3 Handheld TDS Meter With Carrying Case, 0 - 9990 ppm TDS Measurement Range, 1 ppm Resolution, +/- 2% Readout Accuracy: Home Improvement).


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## Bobbybills (Nov 30, 2015)

@Edward
Ok, I understand. I have a scale made for measuring gunpowder so it is accurate to .000g. Salt is cheap so I will go it both ways just to see.


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## mistergreen (Dec 9, 2006)

1 g of salt in 1 Liter should give you 1000 ppm. You can calibrate your meter with this formula. 1mg/L = 1 ppm tds.
Use distilled water of course.

Sent from my iPad using Tapatalk HD


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## Edward (Apr 11, 2005)

*Calibration & verification of TDS and Conductivity meters*

Calibration & verification of TDS and Conductivity meters can be done with kitchen salt.

Read RO water
Dissolve 3.0 grams of kitchen salt in 1000 ml RO
Take 100 ml
Add 900 ml RO water into the 100 ml
Read salt solution

Result = salt solution – RO water

Expected readings

300 ppm as NaCl
318 ppm as KCl
419 ppm as “442”
614 µS

Test can be done with kitchen iodized salt, pickling salt or sea salt dissolved in distilled or RO water.


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## Bobbybills (Nov 30, 2015)

@Edward

300mg in 1000ml distilled water

TDS-4 HM Digital = 416ppm
AP2 HM Digital = 738µS

both at 67Deg F

UPDATE: I did not have enough distilled to dilute 3g 1:10 so I will try again doing it that way. My numbers are way off.


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## Edward (Apr 11, 2005)

Bobbybills said:


> @Edward
> 
> 300mg in 1000ml distilled water
> 
> ...


Wow you are fast!
Did you subtract RO readings? No, that is still too high …


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## Bobbybills (Nov 30, 2015)

I was in the process. I used distilled water, not RO, µS was 1.


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## Edward (Apr 11, 2005)

You have RO at home and it’s free!


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## Bobbybills (Nov 30, 2015)

OK, took 3grams in 1000ml RO, then added 900ml RO to 100ml.

RO = 15ppm 8µS
300mg in 1000ml = 327ppm and 593µS


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## Edward (Apr 11, 2005)

Bobbybills said:


> ... RO = 15ppm 8µS ...


 Typo?


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## Bobbybills (Nov 30, 2015)

yes, backwards 15µS 8ppm


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## Edward (Apr 11, 2005)

Bobby, good job
Your NaCl ppm meter is reading little high, 319 instead of 300.
Your Conductivity µS meter is reading little low, 578 instead of 614.

I noticed, your µS to ppm as NaCl was always at 1.88. It should be 2.05. Today’s test confirms it.
Time to calibrate?

Thank you!


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## Bobbybills (Nov 30, 2015)

I see that and will look into it. I did notice that the readings for both units seemed to drift down over time so I tried to allow sufficient time for the readings to stabilize but that could add to human error. Also the 1000ml beaker has room for error. The increase in ppm of 6% could easily be within the margin of error, so let's say the actual starting volume was 970 ml and when I diluted that, I used 103ml instead of 100 to make the 1000ml, between the two errors would equal 6%. Lastly, I am using measuring devices that start out with very high readubgs and if not cleaned properly, leave behind solids after the water evaporates which would affect the next reading after those remaining solids are put back into solution. I would think all of these things affect the accuracy.

Why one is higher and the other lower, not sure about that yet. Thanks for your continued education.


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## Immortal1 (Feb 18, 2015)

Well, based on the numbers listed above I am guessing my scale is not as accurate as it should be.
I measured out 30g of normal kitchen salt using 2 different containers (is scale more accurate with a light container or heavier container).
I then poured the salt into something I am guessing all of us have - 5ml glass vials from an API test kit (see pic below).

Then the 30g of salt was poured into 1,000ml RO water.
100ml was removed and added to 900ml RO water.
100ml was again removed and added to another 900ml RO water.
Results:

Obtained RO = 5ppm NaCl or 10 µs/CM
The solution measured 357ppm NaCl or 714 µs/CM @ 69 degrees F
Increase = 352ppm NaCl or 704 µs/CM (interesting, my numbers seem to be increasing some each time I make a reading over 10 minute span)

So, I am gathering that either my meter is reading high or my scale sucks and I started out with too much salt. For those of you out there with regular table salt and access to a good scale AND standard 5ml vials, can you show me how much salt I should be using?


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## Maryland Guppy (Dec 6, 2014)

Since this experiment caught my interest.

Tested .3g in 1000ml cold water tap about 58F. TDS tap = 67ppm.
3 tests were very poor and all over the place.
No repeat ability.

2nd set of 3 tests @ 80F. Tap TDS = 97ppm.
Results of 402, 398, and 394. I can live with this.

80F was closer to tank temps for test purposes.
Cheap evilbay tester bundled with pH probe for $16.

I will now see what 3 grams looks like in test tube.









Now I am not sure 3 or 30 grams. This is 3 grams.


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## Edward (Apr 11, 2005)

Immortal1
Physical quantity is misleading because the grain sizes vary.

Your three measurements are correctly in the same proper ratio of 1 : 2, ppm : µS. The only thing is they are both 15% too high. The 300 mg salt in 1L should read as 300 ppm as NaCl and 614 µS. 

You can test your scale with water. 
100 ml = 100 grams


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## Immortal1 (Feb 18, 2015)

109ml water = 100 grams
go figure. Time to find a better scale


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## Edward (Apr 11, 2005)

Maryland Guppy
You got the correct 300 ppm as NaCl increase with 300 mg of salt in 1L. It is well calibrated.

The repeatability issue is caused by dirty probe electrodes. Dipping the meter into methyl alcohol or Vodka for few hours will clean it up.


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## Immortal1 (Feb 18, 2015)

Wouldn't that make the Vodka taste bad? ;-) 
Otherwise, good info to know.


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## Maryland Guppy (Dec 6, 2014)

Edward said:


> Maryland Guppy
> You got the correct 300 ppm as NaCl increase with 300 mg of salt in 1L. It is well calibrated.


I wouldn't go so far to say it is well calibrated.
It is an ultra-cheap meter but it works per say.

I perform WC's @ 300 ppm.
Due to the fact I have a concrete hardscape that is constantly dissolving.
Don't remember where the 300ppm number even came from.
Some uneducated tested of my own I guess.
At least I do work with a number in mind.

Hardscape has taken 15 months to mellow out on dissolving.


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## Immortal1 (Feb 18, 2015)

Well I will be - I actually got 301ppm NaCl on my TDS meter!
Now for the rest of the story....
I bought a new (cheap) digital scale that measures with an accuracy of 0.1grams (nice). Then I took my 100ml of water and added it to a container already zeroed out on the scale and I get 94 or 95 grams - errrrrr. 
So, I figured what the heck. lets assume the glass measuring device is less accurate than the digital scale. At the same time, why not verify the 1,000 ml container is also accurate. Well, if you look closely at the plastic container it was not very accurate. 
My calibration method went like this - measure out 100g of water 10 separate times and add that quantity into the plastic container (noting where 900g of water was).
Then I added distilled water to the 1,000g mark on the plastic bottle. Measured out 30g of table salt and added it to the 1,000g of water.
As Edward instructed, I drained off 100g of salted water, then added that to 900g of fresh distilled water.

Then drained off another 100g of that mixture and added it to a fresh 900g of distilled water.
Then I drained off enough water from the container to get an accurate reading.

Distilled water measured 1ppm NaCl at 71 degrees
And as you can see in the picture, I am at 301ppm NaCl at 71 degrees for my mixture. 
Needles to say, I was kinda shocked.
cm
As for the EC reading, that measured out to 604 µs/CM at 71 degrees with a starting point of 4 µs/CM for fresh distilled water.


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## Edward (Apr 11, 2005)

Excellent Immortal1


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## Immortal1 (Feb 18, 2015)

LOL, seems to me it was actually dumb luck. But, atleast I know the meter is likely accurate enough to be useful on my tanks.

Hopefully my method of generating the mixture will be helpful to others.


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## bsherwood (Nov 22, 2007)

ok, so ...I bought a tds meter that measures in uS units....

new question...when I read various websites and they talk about "TDS" of 80-200 being acceptable, what units are they talking about ? ppm or uS???


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## Edward (Apr 11, 2005)

bsherwood said:


> ok, so ...I bought a tds meter that measures in uS units....
> 
> new question...when I read various websites and they talk about "TDS" of 80-200 being acceptable, what units are they talking about ? ppm or uS???


 Maybe they are talking about ppm as NaCl, but who knows, they didn’t say.
This is the problem I am talking about in this thread. There are TDS meters in ppm as NaCl, ppm as “442” and ppm as KCl. 

All ppm meters read as some unrelated equivalent to aquarium water composition. But, that’s what people want to use so we have to adapt. The question remains, what kind of ppm are they talking about? I don’t know but most assume ppm as NaCl. 

300 ppm as NaCl 
318 ppm as KCl
419 ppm as “442”

614 µS (micro Siemens)

All above represent the same water conductivity.

So the 80 – 200 range in ppm is so huge it doesn’t really mean anything critical. The 80 is about soft tap and 200 is medium to hard tap. 
Sorry for the confusion.


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## mistergreen (Dec 9, 2006)

Tds is measured in ppm for fish and such. I posted a link a few pages back explaining all this.


Sent from my iPad using Tapatalk HD


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## Edward (Apr 11, 2005)

mistergreen said:


> Tds is measured in ppm for fish and such. I posted a link a few pages back explaining all this.


 Can we see your fertilizer application?


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## mistergreen (Dec 9, 2006)

Edward said:


> Can we see your fertilizer application?


It's on the apple store as mistergreen's fertilizer calculator.
I'll add salt and it's TDS to the list. I can't aded uS unless I know the ppm per uS, I guess. I'll have to play with it.


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## Edward (Apr 11, 2005)

mistergreen said:


> It's on the apple store as mistergreen's fertilizer calculator.


 Making $ profit on free aquarium fertilizing systems???


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## mistergreen (Dec 9, 2006)

Edward said:


> Making $ profit on free aquarium fertilizing systems???


No, There's a $100 apple fee every year.


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## ibebian (Jan 11, 2016)

Edward said:


> TDS in ppm is for kitchen salt applications, not for aquariums. Aquariums use µS because of the solids involved.
> 
> You can switch the TDS meter to µS reading and get a different value.




I didn't know this, could you elaborate a little further why micro Siemens is the right measurement unit? Thanks!


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## ibebian (Jan 11, 2016)

mistergreen said:


> Tds is measured in ppm for fish and such. I posted a link a few pages back explaining all this.
> 
> 
> Sent from my iPad using Tapatalk HD




So which should it be?


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## Edward (Apr 11, 2005)

ibebian said:


> I didn't know this, could you elaborate a little further why micro Siemens is the right measurement unit? Thanks!


 Hi
In this thread post #40 I have demonstrated how chemical compounds vary in ability to conduct an electric current. This current and voltage applied is used to calculate electrical conductance. The unit for conductance is Siemens. This is why µS (micro Siemens) meters are the real conductivity meters.

When industries dealing with single salt solutions wanted to use these Siemens meters to monitor chemical concentrations they had to use written conversion tables from µS to ppm. Then one day, they decided to build-in the conversion tables in the actual conductivity meters. Meters that can read ppm as NaCl or any salt of choice.

However, aquarium water column is *no* single salt solution. 

For more there is Wiki.


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## heel4you (Mar 8, 2015)

So, Meters that can read ppm as NaCl can be used for TDS? 
Thank you


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## Immortal1 (Feb 18, 2015)

heel4you said:


> So, Meters that can read ppm as NaCl can be used for TDS?
> Thank you


For what its worth, that is what I am using and I was successful in accurately reading a specific salt solution. 

I actual practice, it does seem to work well for my tanks.


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## Edward (Apr 11, 2005)

heel4you said:


> So, Meters that can read ppm as NaCl can be used for TDS?


 So, money that can be counted in Japanese Yen can be used as currency?

Yes. 

US Dollar, CDN Dollar, Japanese Yen and Australian Dollar are currencies. But 100 US Dollars is not equal 100 Japanese Yen. Just like TDS 100 ppm as NaCl is not equal TDS 100 ppm as KCl.


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## Byeiksar (Dec 1, 2015)

Really sorry to awake this old post,,, now i would like to buy a tds meter for my shrimp tank. I should buy meter with ppm unit or μs unit? I did read the whole thread but due to my limited english,i dont get clear answer which to buy :crying:..and I still need to calibrate the meter with table salt,right?? somebody please advise.


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## Immortal1 (Feb 18, 2015)

The meter that I purchased reads both ppm and μs, also Celsius and Fahrenheit. I calibrated mine with table salt by did not have to make any changes as the calibration from the manufacture was good.


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## Byeiksar (Dec 1, 2015)

Immortal1 said:


> The meter that I purchased reads both ppm and μs, also Celsius and Fahrenheit. I calibrated mine with table salt by did not have to make any changes as the calibration from the manufacture was good.


 Most meter I see show in ppm so I can use them right? how can we know factory calibrated is correct ?by checking with table salt?:help:
which unit is supposed to be used? ppm or μs?


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## ibebian (Jan 11, 2016)

Edward said:


> So, money that can be counted in Japanese Yen can be used as currency?
> 
> Yes.
> 
> US Dollar, CDN Dollar, Japanese Yen and Australian Dollar are currencies. But 100 US Dollars is not equal 100 Japanese Yen. Just like TDS 100 ppm as NaCl is not equal TDS 100 ppm as KCl.


Interesting, so we want microsiemens to measure conductance across all salts, and I presume other compounds as well. So when it comes to our aquariums, what are some of these other compounds that would be measured? Is NaCl for the ppm conversion chosen as de facto because that most closely resembles the various organic material common to our water column?


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## jw.cS (Jan 13, 2005)

Byeiksar said:


> Most meter I see show in ppm so I can use them right? how can we know factory calibrated is correct ?by checking with table salt?:help:
> which unit is supposed to be used? ppm or μs?


TDS "should" be measured in microSiemen for ease of communication. However, most numbers that you find online are (I bet) in ppm NaCl because those are the cheapest meters and that's the way these things are marketed. From my research when I bought one, ppm is marketed as "TDS Meter" while microSiemen is marketed as "EC Meter." The price points quoted by "experts" are for the TDS meters. EC meters are generally more expensive. Furthermore, the numbers quoted on shrimp forums after adding certain things (like GH booster) runs more comparable with ppm NaCl TDS meters than the microSiemen EC meters. So if you see TDS numbers that are not followed by units then you can safely bet it's in ppm. *shrugs*

Soooo, what is one to do? Buy an EC Meter that will give results in BOTH ppm and microSiemen. The difference in price is 5-10 USD: chump change, compared to the other things that we buy. Search for "EC Meter" and you'll get more results than "TDS Meter." They both measure the same things.


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## dukydaf (Dec 27, 2004)

I think TDS should indeed be reported in ppm (mg/L). Think about what is the name/purpose of the test... It is used to provide the Total Dissolved Solids concentration in a volume of water, meaning 

" a measure of the sum of all inorganic and organic substances in a liquid in molecular, ionized or micro-granular colloidal suspended form."

If you want to report the concentration of a substance you measure how many grams/moles etc are added to what volume of water, not how many Siemen, thus mg/L makes sense. 

The main confusion comes from the way we test for it, using conductivity of the dissolved ionized solids in the water. This conductivity is indeed measured in μS and then converted using (hopefully) a standard calibration curve to ppm of Something in water. Furthermore, some organics will be ignored by this test because they do not increase conductivity. 

The serious way to do it in the lab is to use the gravimetric method. Basically, you evaporate the water out of all the molecules at 180°C and weight the leftovers. Now, using this method you can see why TDS in the scientific community is reported in mg/L.

I believe you are right, most TDS measurement use ppm, but ppm of what ? Sadly this test is poorly understood and recommended as a basis to do water changes, keep shrimps etc. Good to test , but like the pH test, do not base your wc and nutrients on it. A TDS number should always have the unit of measurement besides it eg. ppm NaCl . 

Do not use table salt for calibration as it is rarely pure NaCl. If you want to do your own calibration use lab grade NaCl or KCl, whichever the manufacturer of the meter used.


Further reading: 
TDS and EC Calibration Solutions - HM Digital
http://www.iccontrols.com/files/TDS_Measurement.pdf


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