RO water TDS Level

[Niks76]

My tap water starts out at about 320 and after the three stage RO unit ends up at 10. Is this good enough for a freshwater planted tank or should I get a DI add on for it? Thanks.

 

[dmolavi]

That is fine for FW. If you went with a DI, you'd have to use something like Seachem's Replenish (Seachem. Replenish) to remineralize the water, otherwise your livestock would perish.

 

[Niks76]

Thanks. I did get seachem equilibrium. I just didn't know if my target should be 0 TDS or not before putting the seachem in.

 

[dmolavi]

I have a lightly planted FW tank and use straight up tap for it (with Prime). I've had no issues, but do weekly PWC.

I only use RO/DI in my SW tank.

 

[J.Mcpeak]

I re buffer my RO/di with tap water, sounds a bit backwards I know, never had a problem. 010 TDS is very acid water, incapable of sustaining most aquatic life. If you have alkaline water the correct combination can be used to make water from 0 to tap water TDS. For me roughly 50:50 gives TDS 120 approx to neutral pH. Water from tap is still de-chlorinated.

This is balanced and safe in freshwater up to TDS 030. Then the Di resin needs changing as it messes the ratio up considerably.

TDS and Gh are basically the same thing.

 

[dragonfisher33]

agree. RO or RO/DI is usually reserved for SW tanks or FW with delicate fish such as discus. if you don't have these two types of tanks, a regular tap water from faucet should suffice. also, the minerals and chemicals such as phosphate in the water are great for planted tanks.

 

[dmolavi]

010 TDS is very acid water, incapable of sustaining most aquatic life.

This is not true. TDS doesn't govern the acidity/alkalinity of the water, pH does, which is a logarithmic measure of the amount of hydrogen/hydroxide ions in the water.

Edit: I shouldn't say pH "does" govern the acidity/alkalinity of water...it doesn't. It's a measure of the acidity/alkalinity.

 

[dmolavi]

To expand...from a chemical engineering source:
"There is NO relationship between pH and TDS. Let us imagine a solution of an acid salt, say sodium bisufate (a.k.a. sodium hydrogen sulfate). No matter what its concentration (TDS), it will have a low ph (< 7.0). Now take an alkaline salt solution, say sodium carbonate. Again no matter the concentration, the pH will be high (>7.0). Even for a given solution, there is nothing approaching a linear relationship. Take pure water and drop a flake of sodium hydroxide into it. The pH will skyrocket. As you add more caustic, the pH will continue to rise to a point, but it will do so much more slowly."

 

[J.Mcpeak]

This is not true. TDS doesn't govern the acidity/alkalinity of the water, pH does, which is a logarithmic measure of the amount of hydrogen/hydroxide ions in the water.

Test a sample of RO/di water at 010 it is acidic.

Incorrect, PH is a measure of the balance of those ions. The amount of TDS will buffer the water up down accordingly. TDS is hardness. Total dissolved solids.

 

[dmolavi]

I know what TDS is. Hardness is KH and GH, not pH. Read my post above yours with the example.

 

[J.Mcpeak]

I know what TDS is. Hardness is KH and GH, not pH. Read my post above yours with the example.

Where exactly did I state hardness is pH? TDS is Gh, Kh is the carbonic element of gh responsible for buffering the water which in turn balances the pH up or down.

Edit-
I understand that pH is a balance of 8 ions positive and negative, 4 of each. Kh is the buffering capability of given sample.

 

[dmolavi]

Buffering is just the ability of the pH to change. If you have a lot of buffering capacity (high KH), you resist pH change. A low buffering capacity (low KH) is more susceptible to shifts in pH.

pH and pOH: Crash Course Chemistry #30 - YouTube

Buffers, the Acid Rain Slayer: Crash Course Chemistry #31 - YouTube

 

[dmolavi]

Also, my zero TDS from my RO/DI system has a pH of 7.

 

[J.Mcpeak]

ShrimpNow !!! - Water Parameters: Understanding pH, GH, KH and others

 

[dmolavi]

From your own link:
KH (Carbonate Hardness - Karbonathärte in German)
Carbonate Hardness measures the amount of carbonates and bicarbonates in water, expressed in German degrees of hardness (dKH). The term 'hardness' in KH is somewhat confusing because it does not actually measure hardness, but rather the alkalinity (buffering capacity - ability to neutralize acids) of a solution to resist a pH change. The higher the KH, the more stable and resistant your water is to pH swings. A KH of 2-3dKH is generally accepted as the minimum to maintain a stable pH.

IOW, a high KH (or TDS, as you're connecting the dots in your posts), does *not* equate to a high pH. Just a better ability to resist swings in pH.

 

[J.Mcpeak]

A sample of 0 TDS RO/DI water left for 24hrs.
Any tests to produced or tap water should be made with this timeframe in mind.

Initially it will measure 7 neutral that is the result of the deionising resin. Without any buffers the water will be affected by CO2 in the atmosphere which will shift the pH to acid. The equipment I own does not allow me to test below pH 4.5.

Edit- you are repeating me consistently. See post #11 & # 15

Edit, edit- add post #12

 

[J.Mcpeak]

To expand...from a chemical engineering source:
"There is NO relationship between pH and TDS. Let us imagine a solution of an acid salt, say sodium bisufate (a.k.a. sodium hydrogen sulfate). No matter what its concentration (TDS), it will have a low ph (< 7.0). Now take an alkaline salt solution, say sodium carbonate. Again no matter the concentration, the pH will be high (>7.0). Even for a given solution, there is nothing approaching a linear relationship. Take pure water and drop a flake of sodium hydroxide into it. The pH will skyrocket. As you add more caustic, the pH will continue to rise to a point, but it will do so much more slowly."

So, it would appear that yes there is a relationship between pH and TDS and a really rather significant one.

If you quote scientific reference material, I would say have a fundamental grasp on the knowledge contained therein.
To add an alkaline or acid sulfate to any body of water will obviously change its chemical characteristics in favour of the substance added.

I say it not only because I believe it, but also because I fully understand it. I also carry out my own research and present those facts based on a result of that research. If I struggle with my observations I source the relevant papers to provide me with the answers necessary to complete or conclude my trials.

Any questions?

 

[J.Mcpeak]

From your own link:
KH (Carbonate Hardness - Karbonathärte in German)
Carbonate Hardness measures the amount of carbonates and bicarbonates in water, expressed in German degrees of hardness (dKH). The term 'hardness' in KH is somewhat confusing because it does not actually measure hardness, but rather the alkalinity (buffering capacity - ability to neutralize acids) of a solution to resist a pH change. The higher the KH, the more stable and resistant your water is to pH swings. A KH of 2-3dKH is generally accepted as the minimum to maintain a stable pH.

IOW, a high KH (or TDS, as you're connecting the dots in your posts), does *not* equate to a high pH. Just a better ability to resist swings in pH.

Kh is not TDS, gH is TDS. Again I never stated kh is TDS.
If the water sample contains a low buffering ability it will change to acidic water carbon dioxide (CO2) is the reason for this.
Carbon dioxide is known to be acidic.
The buffering ability of the water neutralises this acidic compound I refer to, CO2.

So to conclude a high kH does in fact result in a high pH.
It's all there if you read it. I will re-highlight it for your benefit.

(buffering capacity - ability to neutralize acids)

Another clue, alkalinity, not acidity.

See post #11

 

[aqua_chem]

You're both wrong.


J.Mcpeak: You seem to not understand the definitions of some terms. GH is the total calcium and magnesium concentration. KH is total carbonate (HCO3- + CO3--) concentration. The two are not inherently related. You can freely increase one without increasing the other. TDS is total solids in solution. It's the sum of GH, KH, non-GH/KH ions (notable sodium, potassium, and chloride), organic molecules, and small particles. It is related to pH (see below), but not in the way you describe. In your examples, it's KH that's controlling pH, not TDS per se.

dmolavi: two things.

IOW, a high KH (or TDS, as you're connecting the dots in your posts), does *not* equate to a high pH. Just a better ability to resist swings in pH.

I don't think this is a fair assessment. Higher KH will increase pH independent of other factors. It's not the only thing that determines pH (eg, tannic acids from DW, organic acids from fish, acids produced from nitrification), but in raw RO water it's definitely the main contributor to pH. It's no coincidence that areas with high pH generally have high KH and areas with low pH have low pH (although there's some cause/effect problems with the latter).

Second:

This is not true. TDS doesn't govern the acidity/alkalinity of the water, pH does, which is a logarithmic measure of the amount of hydrogen/hydroxide ions in the water.

Edit: I shouldn't say pH "does" govern the acidity/alkalinity of water...it doesn't. It's a measure of the acidity/alkalinity.

There is NO relationship between pH and TDS. Let us imagine a solution of an acid salt, say sodium bisufate (a.k.a. sodium hydrogen sulfate). No matter what its concentration (TDS), it will have a low ph (< 7.0). Now take an alkaline salt solution, say sodium carbonate. Again no matter the concentration, the pH will be high (>7.0). Even for a given solution, there is nothing approaching a linear relationship. Take pure water and drop a flake of sodium hydroxide into it. The pH will skyrocket. As you add more caustic, the pH will continue to rise to a point, but it will do so much more slowly."

This is what we teach non-chemistry/physics undergraduates. It's what we would call a "mostly true lie". In reality, pH isn't a measure of the concentration of hydrogen ions, it's a measure of their activity. High TDS can significantly contribute to ionic strength, which can significantly change pH under conditions of high TDS (assuming it's composed of mostly ions). This isn't widely appreciate by the aquarium hobby (I only found one acknowledgment of it), but it will happen to low-TDS fishkeepers who calibrate their meters in highly buffered calibration solutions (ie high ionic concentration) and then try to measure the pH of minimally buffered tanks.

 

[J.Mcpeak]

You're both wrong.


J.Mcpeak: You seem to not understand the definitions of some terms. GH is the total calcium and magnesium concentration. KH is total carbonate (HCO3- + CO3--) concentration. The two are not inherently related. You can freely increase one without increasing the other. TDS is total solids in solution. It's the sum of GH, KH, non-GH/KH ions (notable sodium, potassium, and chloride), organic molecules, and small particles. It is related to pH (see below), but not in the way you describe. In your examples, it's KH that's controlling pH, not TDS per se.

dmolavi: two things.



I don't think this is a fair assessment. Higher KH will increase pH independent of other factors. It's not the only thing that determines pH (eg, tannic acids from DW, organic acids from fish, acids produced from nitrification), but in raw RO water it's definitely the main contributor to pH. It's no coincidence that areas with high pH generally have high KH and areas with low pH have low pH (although there's some cause/effect problems with the latter).

Second:






This is what we teach non-chemistry/physics undergraduates. It's what we would call a "mostly true lie". In reality, pH isn't a measure of the concentration of hydrogen ions, it's a measure of their activity. High TDS can significantly contribute to ionic strength, which can significantly change pH under conditions of high TDS (assuming it's composed of mostly ions). This isn't widely appreciate by the aquarium hobby (I only found one acknowledgment of it), but it will happen to low-TDS fishkeepers who calibrate their meters in highly buffered calibration solutions (ie high ionic concentration) and then try to measure the pH of minimally buffered tanks.

Tds is total dissolved solids, I said that.

I also mentioned kh being the carbonic element of gH. By my tests tds and gh are similar numbers, close enough to be the same.
I used a TDS stick and liquid gH test. I understood it to be gH is the hardness of the water overall, general hardness, kH is as previously stated, the carbon element responsible for buffering.

I did not include organic compounds as this thread was directed at RO water, I only mentioned the co2 in the atmosphere. In any case the KH will be responsible for stabilising or countering all organic compounds as most if not all are acidic.

However it seems I still have much to learn!

It would seem TDS includes other elements beyond gH/KH. Perhaps this is why the numbers are only close?

EDIT 1- gH includes KH. Post #11.
Post #9 misleading (inaccurate)
The amount of TDS will buffer the water up down accordingly. TDS is hardness. This is Wrong.

EDIT 2-
"There are several ways to define acids and bases, but pH and pOH only refers to hydrogen ion concentration and hydroxide ion concentration, respectively. pH and pOH are only meaningful when applied to aqueous (water-based) solution."

Anne Marie Helmenstine, Ph.D.
(Several sources confirm edit 2)