# New to TDS



## davgriggs (Apr 11, 2018)

I’m using a TDS meter for first time. Tested my tap water which was 275. Tank water after 40% water change was 325. Use PPS pro ferts as per the instructions. No wood. Fluorite substrate. Use daily API CO2 booster (ran out Of pressurized CO2 but will buy some soon), feed once a day. 12 gallon tank. Fully planted with about 1/4 of substrate carpeted. 3 dwarf Gouramis, 5 neon tetras, 5 Ottos, 5 Amano shrimp, 9 Nirite and bunch of hitchhiker snails. Nitrites and ammonia pretty much always zero. Nitrates around 30 after weekly 40% water change. 
-
Any comments on my TDS would be appreciated. What would be considered too high for my situation. I am hoping to use the meter to gauge when to do water change and such.


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## MCFC (Feb 12, 2017)

davgriggs said:


> weekly 40% water change.


Why change?


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## Deanna (Feb 15, 2017)

Almost every substance added to the water will increase TDS: water conditioner, fish foods, plant fertilizers, medications, water adjustment products, etc. Often, if your GH is high, this will be the major component of a TDS reading.

A TDS range of 100 - 400 is acceptable, but targeting the lower end of the range is best. Be careful about TDS changes greater than a maximum of 50 ppm or 10%, whichever is greater. The osmotic pressure change can cause TDS shock in fish (what we used to - incorrectly - think of as pH shock). Allow a few days between changes of these magnitudes.


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## madcrafted (Dec 23, 2017)

That's a pretty heavy bioload for a 12 gallon tank. TDS readings only help when you know the exact composition of your water. A water quality report might offer some insight. You'd be better off using nitrate readings to determine water changes with your particular tank.


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## Edward (Apr 11, 2005)

davgriggs said:


> Tested my tap water which was 275. … Any comments on my TDS would be appreciated. What would be considered too high for my situation.


 Can’t say because you didn’t include what kind of TDS value, µS or ppm NaCl? There is more than one TDS system. 


davgriggs said:


> I am hoping to use the meter to gauge when to do water change and such.


 Greater TDS difference between tap and aquarium greater the need for water changes.


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## davgriggs (Apr 11, 2018)

my meter measures in ppm


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## Edward (Apr 11, 2005)

Tap TDS 275 ppm NaCl (564 µS) is very high. It is an indication of high GH and KH, or NaCl water softener.


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## Tiger15 (Jan 7, 2018)

What TDS meter measures is electrical conductivity in uS/m, but for easy understanding, it is converted to equivalent ppm of Na or Ca using factors of 0.5 to 0.65 respectively, or some other factors based on assumption of the ions present. Your instruction may say what factor is used, but more often not. So comparing one tds value to another is not one to one, as it depends on the ions present. TDS is proxy of many things, such as salinity, hardness, level of pollution, or how long you haven’t done WC.


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## Tyrant46290 (Jul 21, 2018)

Dechlorinater will raise water too. TDS is basically a measurement of anything and everything in the water all in 1 reading. Completely useless without knowing what is in it.


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## tamsin (Jan 12, 2011)

Edward said:


> Tap TDS 275 ppm NaCl (564 µS) is very high. It is an indication of high GH and KH, or NaCl water softener.



Depends where you live. My tap TDS is 400 so I'd consider 275 hard but nothing to panic over 



If your water changes keep on top of things you'd expect your TDS to be about the TDS of your tap plus 2 x the amount your ferts raise the TDS between changes. Measure your TDS before and after you add ferts (give it time to mix after). That's how much the ferts contribute.


I wouldn't worry too much about the actual number though - TDS measures all the 'stuff' but doesn't tell you what it is. What it does tell you is if you are keeping things stable. So measure over time, and if you see it gradually creep up you know you need to change a bit more water. Roughly, you want to reset your TDS at each water change so over time it stays stable. The stable number will be unique to you and will generally be a bit higher than your tap.


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## dukydaf (Dec 27, 2004)

Tyrant46290 said:


> Dechlorinater will raise water too. TDS is basically a measurement of anything and everything in the water all in 1 reading. Completely useless without knowing what is in it.


I think this is a good summary of TDS in so far it concerns aquarium keeping. I would add some things would not even register on a TDS meter. And as mentioned a TDS pen does not even measure TDS but tries to give equiv. with an unknown(to us) curve.

Use it to check if the RO unit works well, you got your remineralizer dosing right in pure RODI water and if the cooling water needs changing.

Different things can give the same TDS reading. Even for the things that the TDS can detect, the ratios between them can change in the aquarium while the TDS 'remains stable'. 

Some people have argued a long time ago that you should do water changes based on the change in TDS. I raise an eyebrow and smile. I won't go into the arguments again, but take into consideration what was written above and in others' post, and decide if it is still good for your application.


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## AdamRT (Jan 23, 2018)

For my new build I am using conductivity or ec, a reliable method of measuring tds as long as you know the conversion factor for your meter (the Hanna “dist” series uses a .5 conversion, so a measurement of 200 microsiemens on the meter represents a tds of 100 ppm), as the guiding metric for when I need to dose ferts, perform water changes, etc.. 

I’ve found ec/tds to be the most reliable and simple way to determine when adjustments to the water are necessary, and would definitely recommend it to anyone looking to fine tune their dosing/water change routine without having to test a million different parameters. It works whether you are using tap water or ro/di (although I think it’s an even better indicator when using ro/di because you can control the exact make up of the tds in your tank). 

With tap water (and rodi for that matter) you need to establish two baseline tds readings in order to use it as a determinitive metric- source water and baseline tank water. Let’s say your water comes out the tap with a tds of 150ppm (or an ec of 300 microsiemens), and the water in your tank before ever dosing ferts or immediately after a 50% wc has a tds of 250ppm due to fish waste, nutrients released by substrate/driftwood/decaying plant matter. 

The 250ppm number is the baseline in this example. If you’re using a dosing method like pps or pps pro- you would add ferts at the suggested rates until you observe a 100ppm increase in your baseline tds (350ppm in this example). Once your tds has increased by 100ppm, it is now time to do a water change to reset the tank back to its baseline of 250 (or as close as you can get).

This is where using tap water can get tricky- if you are replacing the 350ppm water with tap water that has a tds of 150ppm, you will need to change far more water to get back to your baseline than you would if you were using ultra low tds rodi water. My rodi unit puts out water with a tds of 1-2ppm which is exceptionally low for a home purification system. I won’t get in to the math, but one can clearly see that using 2ppm water for a change will be much more efficient at getting you back to your baseline than if you use water that’s 150ppm. You also have the benefit of knowing exactly what elements are responsible for a given tds reading when starting from 0 (or close to it) because you are adding them in. With tap water, the tds could be the result of any one or a combination of a number of elements that we cannot control for (in my town we have pretty high NACL and iron content in our tap, so those three elements are the main sources of tds but there are certainly others like calcium, magnesium, silica, etc. that also contribute. I strongly suggest going on your towns website and accessing your most recent water quality report to get an idea of what’s in your tap water). 

Most of the elements that would raise tds in your tap water are beneficial nutrients for plants, but it’s impossible to determine the concentrations of each without expernsive testing or very detailed and accurate town water reports. Again, this is why I prefer rodi water when using ec or tds as the determining factor. However, as long as you have a baseline to work from and your tap tds isn’t higher than your target baseline tank tds, tap water or a mix of tap and rodi can work. 

One last note on baseline tds- I’ve seen a lot of people both here and on other sites claim that tds values in and of themselves are worthless measurements- this may be true in a tank with no fish, but if you do keep fish in your fish tank lol the claim that tds is a worthless measurement is completely incorrect and I will gladly argue that point with anyone who wishes to do so. 

Most of the fish that we commonly stock in our planted tanks (most tetras, rasboras, gouramis, non-rift lake cichlids, etc.) have evolved to live in low tds conditions and rely on the relatively pure water in which they live to remove contaminants from their bodies. A classic softwater tetra like a neon or cardinal will producd as much as 3.5 times their body weight in urine every day. They take in the ultra low tds water from their surroundings and use it to flush nitrates and other nutrients from their bodies. This works because they are adapted to the relative osmotic pressure of the low tds eater in which they live. If you place these fish in conditions where the tds is approaching the levels inside their bodies, their internal organs must work much harder to purge the nutrients from their bodies which places undue strain on their kidneys and liver, which in turn stresses the fish and weakens their immune system, shortening their lifespan and making them far more succeptible to disease. 

Some Amazon biotopes have natural tds levels as low as 10-20ppm! Aquarists looking to succefully keep and or breed fish from such regions almost always rely on a rodi system for their water. Even then, levels this low are not really attainable in a planted tank setting, and would be problematic for the plants. You also have to make sure you provide enough mineral content to allow the fish to perform their metabolic functions. 

Because I keep tetras from very low tds environments, I try to keep my baseline tds at around 120-150ppm and will change the water once it hits 200ppm. This is just the number Ive settled on based on what works for my fish and plants but everyone has to come up with a number that works for their set up. Observation of plant and fish health is the best way to make that determination. 

There are plenty of people who keep tetras like rummy nose, cardinals, neons, etc. with tds that’s double mine, but as previously suggested, I would consider 500ppm to be the absolute cap on what constitutes a healthy low tds environment for Amazonian species and personally would not want to exceed 300ppm. 

Many issues with fish that get attributed to ph swings or hardness are actually caused by osmotic shock, which can occur when fish are subjected to a large swing in osmotic pressure, measured by tds/ec. So contrary to a lot of the info that’s out there I believe tds/ec May be the single most important water parameter we can measure. If you are working with rodi water or known quantities of nutrients in your tap water, no other measurement will be as instructive for dosing and water changes as tds/ec. Period full stop.


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## Edward (Apr 11, 2005)

AdamRT ... Excellent post!



AdamRT said:


> This is where using tap water can get tricky- if you are replacing the 350ppm water with tap water that has a tds of 150ppm, you will need to change far more water to get back to your baseline than you would if you were using ultra low tds rodi water. My rodi unit puts out water with a tds of 1-2ppm which is exceptionally low for a home purification system. I won’t get in to the math, but one can clearly see that using 2ppm water for a change will be much more efficient at getting you back to your baseline than if you use water that’s 150ppm.


Example of cleaning 400L / 100gall aquarium from 300 ppm NaCl / 600 µS to 170 ppm NaCl / 340 µS with tap versus RO.

With 330 µS tap
30% WC, 600 -> 510 (- 90)
30% WC, 510 -> 450 (- 60)
30% WC, 450 -> 410 (- 40)
30% WC, 410 -> 383 (- 27)
30% WC, 383 -> 365 (- 18)
30% WC, 365 -> 353 (- 12)
30% WC, 353 -> 345 (- 8)
30% WC, 345 -> 340 (- 5)
Total amount of used water ≈ 1000 L

With 10 µS RO
30% WC, 600 -> 403 (- 197)
16% WC, 403 -> 340 (- 63)
Amount of used RO clean water ≈ 200 L
Amount of used RO waste water ≈ 800 L at 1 : 4 drain ratio
Total amount of used water ≈ 1000 L

It takes 8 water changes with tap water versus 1.5 with RO water while the total raw water usage remains the same.


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## Discusluv (Dec 24, 2017)

Very helpful


AdamRT said:


> For my new build I am using conductivity or ec, a reliable method of measuring tds as long as you know the conversion factor for your meter (the Hanna “dist” series uses a .5 conversion, so a measurement of 200 microsiemens on the meter represents a tds of 100 ppm), as the guiding metric for when I need to dose ferts, perform water changes, etc..
> 
> I’ve found ec/tds to be the most reliable and simple way to determine when adjustments to the water are necessary, and would definitely recommend it to anyone looking to fine tune their dosing/water change routine without having to test a million different parameters. It works whether you are using tap water or ro/di (although I think it’s an even better indicator when using ro/di because you can control the exact make up of the tds in your tank).
> 
> ...


 Very instructive- thank you. Makes me want to learn exactly what my EC monitor is really telling me on my Fluvel G6 filter. I do look at the changes it gives me before and after a water change, to see the difference of that number, but hadn't really taken the time to understand the implications of what it meant. Right now the EC meter says 230, its been 2 days ago that I did a 75% ( discus tank) water change. I will do another 1 tomorrow or the day after- Ill look to see what it is before and directly after doing so and then after dosing fertilizers. Typically the TDS runs about 115-120 in this tank. It sounds similar to the .5 conversion that you use. 

However, lately ( the last 2 weeks) Ive been adding Equilibrium with water changes because was advised I had a magnesium deficiency in my plants. My KH is 3/GH 5.


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## AdamRT (Jan 23, 2018)

Edward can you please explain how one 30% water change and one 16% water change uses the same amount of water eight 30% water changes? I’m not sure what I’m missing but assuming an aquarium is 100 gallons, each 30% water change is 30 gallons of water. So eight 30 gallon water changes would require 240 gallons of water whereas one 30% change would be 30 gallons and the 16% water change would be 16 gallons for a total of 46 gallons of water changed: 

240 gal > 46 gallons required to hit the target tds. 

So it would appear to me that you can reach your target tds using about 1/5 of the total water when using rodi as opposed to tap. 

Haha Idk what I’m missing, but I’m sure I’m going to feel stupid once you explain it.

Bump: Discusl


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## Tiger15 (Jan 7, 2018)

Live stock is more sensitive to tds than plants. Some soft water fish and shrimp must have low tds to have eggs fertilized, even though adults may do ok in higher tds water. Discus and cardina shrimp keepers need RO water to breed and raise fry sucessfully. In Walstads Ecology book, she reported that Amazon sword from black water habitats do surprising well in hard water aquarium.

In scientific work, tds and conductivity are not interchangeable. Water and wastewater utilities report conductivity values, never tds which is used by lay home owners and aquarists. TDS is a proxy indicator of many things, sort like nitrate is an indicator of pollution in a fish only tank. High nitrate in a fish only tank is not directly toxic to fish, but is an indicator of other toxins that are unknown or untested. 

TDS only measures one parameter directly, osmotic pressure, so in a way is equivalent to salinity in saltwater. If you conduct correlation tests of tds with other parameters, such as hardness, kH, salinity, or how long you haven’t changed water, tds can provide you a quick reading without actually running the parameter test. For example, I run multiple tanks each with different stock level and frequency of WC. A quick tds reading can tell me which tank is over due for WC.


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## AdamRT (Jan 23, 2018)

Discusluv, 

I would suggest going on the fluval website and searching “conductivity”. They have a pretty good breakdown of the implications of ec in aquaria. I’m not sure if the g6 ec meter is intended for fresh or saltwater so it’s important to check the unit of measurement (for low ec/tds scenarios you’d want to use a meter that measures in microsiemens. Because saltwater has a base tds that is an order of magnitude higher than low tds fresh water, it may be measuring in increments that are 1:1000 microsiemens. 

I’m also not sure how accurate/reliable the g6 ec meter is. There are tons of cheap tds and ec meters for sale online, but I ultimately decided to spend a couple dollars more to get the Hanna “dist 3” ec meter for $52. It has a range of 0-2000 microseimens (perfect for this application), it came with calibration fluid and a very nice carrying case, its waterproof, has a one button auto calibtration feature that is very easy to use, measures temp in c or f, and has a .5 conversion factor. 

Considering ec is the only parameter I test for (I have a Hanna ph meter from the same series that I’ll use every once and while too, but not with any regularity any more) I didn’t mind spending a little more to make sure I got a meter that I knew would be accurate. When you think about the money many of us spend on this hobby- $52 seemed like a drop in the bucket to protect an investment of many thousands of dollars. It’s also nice to have a portable meter because it allows you to check the quality of your rodi water (I was very pleased to find that the aquatic life 100gal/day twist-in unit produces water in the 2-4 microseimen, or 1-2ppm tds, range.)

I’ve actually gotten water out of it that reads 0 on the meter, but once it hits the bucket I store it in it shoots up to 1-2ppm tds. I’ve found that if I fill a 5 gallon bucket to about 4 1/3 gallons and add 2 liters of the hottest possible water I can pull from the tap and add a few drops of dechlorinator, it gives me 30-40ppm water that’s right at 76f. It gives me just enough mineral content and keeps the tank temp very stable during water changes. 

But I digress... the point is that if you are going to monitor water quality via ec/tds, I think it’s worth spending a few bucks on a reliable portable meter like the Hanna dist 3. The next step up (either dist 4 or dist 5 not sure which) costs about $100 and will automatically convert ec to tds and display both- Because I am confident in my ability to divide by 2, I opted for the dist 3 and used the $50 I saved to buy a Hanna ph checker. 

Since the conversion is as simple as dividing the reading by two, i didn’t see any reason to spend an extra $50 for the one that reads tds and ec- so the dist 3 is what I’d reccomend. If you don’t need a ph meter, that $50 savings would buy you a Hanna colorimeter or checker for pretty much any parameter you’d like to test: alk, nitrate, nitrite, phosphate, iron (If I hadn’t needed a ph checker- I would have gone with either iron or phosphate). I’ll prolly end up getting those two at some point anyway because I suspect I’m adding more iron than I really need and might be light on phosphates. 

If I was keeping discus or some other sensitive softwater fish, I would keep a really close eye on conductivity/tds and try to limit the swings between water changes as small as possible.


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## Discusluv (Dec 24, 2017)

AdamRT said:


> Discusluv,
> 
> I would suggest going on the fluval website and searching “conductivity”. They have a pretty good breakdown of the implications of ec in aquaria. I’m not sure if the g6 ec meter is intended for fresh or saltwater so it’s important to check the unit of measurement (for low ec/tds scenarios you’d want to use a meter that measures in microsiemens. Because saltwater has a base tds that is an order of magnitude higher than low tds fresh water, it may be measuring in increments that are 1:1000 microsiemens.
> 
> ...


 I dont know how accurate the meter is on that filter as well. I do have a TDS meter -- it is this one:
https://www.amazon.com/gp/product/B000VTQM70/ref=oh_aui_search_detailpage?ie=UTF8&psc=1


I test about once a month with the TDS meter and the range , like I said, is about 115-120 ppm. 

I do need to get an R/O unit , however, because my discus pairs spawn and the eggs are fertilized, yet the eggs calcify.


Edit: Is this the R/O unit you have?

https://www.amazon.com/Aquatic-Life...ocphy=1013763&hvtargid=pla-309694043502&psc=1


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## Tiger15 (Jan 7, 2018)

I think most tds or conductivity meters are accurate, as they meaure electrical current which is highly quantifiable. This is why most tds meters do not require calibration. The problem is the conversion factor from conductivity to tds, as it rarely says what it is. If you use it for internal comparison, it doesn’t matter because you have internal consistency. It matters only if you compare externally, because one tds pen conversion factor can be different from another.


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## Edward (Apr 11, 2005)

AdamRT said:


> Edward can you please explain how one 30% water change and one 16% water change uses the same amount of water eight 30% water changes? I’m not sure what I’m missing but assuming an aquarium is 100 gallons, each 30% water change is 30 gallons of water. So eight 30 gallon water changes would require 240 gallons of water whereas one 30% change would be 30 gallons and the 16% water change would be 16 gallons for a total of 46 gallons of water changed:
> 
> 240 gal > 46 gallons required to hit the target tds.
> 
> So it would appear to me that you can reach your target tds using about 1/5 of the total water when using rodi as opposed to tap.


*Tap: *
Total amount of used water ≈ 1000 L

*RO:* 
Amount of used RO clean water ≈ 200 L
Amount of used RO waste water ≈ 800 L at 1 : 4 drain ratio
Total amount of used water ≈ 1000 L

Total amount of used water = RO clean water + RO waste water


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## mgeorges (Feb 1, 2017)

Edward said:


> AdamRT ... Excellent post!
> 
> 
> 
> ...





AdamRT said:


> Edward can you please explain how one 30% water change and one 16% water change uses the same amount of water eight 30% water changes? I’m not sure what I’m missing but assuming an aquarium is 100 gallons, each 30% water change is 30 gallons of water. So eight 30 gallon water changes would require 240 gallons of water whereas one 30% change would be 30 gallons and the 16% water change would be 16 gallons for a total of 46 gallons of water changed:
> 
> 240 gal > 46 gallons required to hit the target tds.
> 
> ...


Quoted him, answer to your question is bolded. He's including waste water produced by RO unit. It would be more like ~175 L of good water to ~700 L of waste I believe.

Edit: Oops...didn't see the second page where this was already addressed. Sorry.


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## Deanna (Feb 15, 2017)

AdamRT said:


> One last note on baseline tds- I’ve seen a lot of people both here and on other sites claim that tds values in and of themselves are worthless measurements- this may be true in a tank with no fish, but if you do keep fish in your fish tank lol the claim that tds is a worthless measurement is completely incorrect and I will gladly argue that point with anyone who wishes to do so.
> 
> Many issues with fish that get attributed to ph swings or hardness are actually caused by osmotic shock, which can occur when fish are subjected to a large swing in osmotic pressure, measured by tds/ec. So contrary to a lot of the info that’s out there I believe tds/ec May be the single most important water parameter we can measure. If you are working with rodi water or known quantities of nutrients in your tap water, no other measurement will be as instructive for dosing and water changes as tds/ec. Period full stop.


++++1. Those two paragraphs are the most important take-away on the subject. Glad you took the time to document, so exhaustively, this critical. but usually under-appreciated, issue.

Bump:


Discusluv said:


> Edit: Is this the R/O unit you have?


Discusluv,

I'd like to suggest that you take a look at the SpectraPure RO/DI units (spectrapure.com). They are high quality and offer a wide variety of options/prices.


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## AdamRT (Jan 23, 2018)

Hi discusluv,

Yeah the one you linked is the one i have. I’m curious to see how many gallons I get out of it before those numbers start creeping up, but as of right now I love it. It was a breeze to hook up to a y on the washing machine line, and like I said, it’s producing 1-2 ppm water at about 4 gal/hour. 

If you get it just remember to flush the carbon block before adding the membrane with the provided caps, and then make 30 gallons of ro water before adding the di resin. After that you’re good to go.

Bump: Haha! Oh yeah, forgot about the waste water lol. I knew I was gonna feel stupid once it was explained! 

In any case I’d rather add the pure water and control how it’s remineralized and fertilized than roll the dice on the unknown levels of individual elements in my tap. 

The only thing I’m a little worried about is a lack of silica, but I think between all the lava rock and the sediment from the controsoil, I’m ok for a while. Can always supplement if it starts becoming a problem, or cut my ro with tap I guess.


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## Letsfish (Jul 11, 2017)

After reading this post I got a TDS meter. My water fresh out of the tap reads 82 ppm TSD. My aquariums are a 55 gallon,29 gallon and a 10 gallon .The 55 and 29 are dosed with ferts 3X/week along with Excel on the odd days.These 2 tanks are also dossed with CO2.The 10 gallon is a QT and only gets a 50% weekly water change and the other 2 get the same water change and this is done on Wednesdays. The PH from the tap after gassing off is 7.6. After 2 hours of Co2 injection the PH reads 6.5 and the TSD read 190/200 ppm the QT tank reading is 133 ppm. Next Wednesday I will check these numbers before and after the water change.Most of my fish are from the Amazon.


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## Shira (Sep 21, 2019)

I appreciate any help here with KH. My tap water is KH 275 ppm I have a well. My tank water used to be going up to 460. I got rid of all the old gravel which I was told can raise KH. That was funnnn......NOT.....
I put in new gravel and the sezachen red substrate good for plant. 
I have a lot of plants in there, 
After I changed all the gravel, My kh now goes up to 355. 
Really trying to lower KH some more. 
Thanks


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