Water Parameters And Co2

[Spiceweasel69]

Hi

Currently my PH is 8,and my KH is 20. These both seem quite high. I will be installing pressurised co2 this week - am i right in thinking this will drop the PH but not affect KH?

Ta

 

[fatheadminnow]

Why do you think your pH is too high?

A pH of 8.0 is an optimal pH for your beneficial bacteria.

What kind of fish do you have/planning on having?

I am unsure if a higher Co2 level will reduce the pH, but I think I read on here that it does?

-FHM

 

[Colin_T]

With a KH of 20 the CO2 is unlikely to drop the pH. Once the KH is gone then the pH will drop. However, if you have heaps of CO2 in the tank, then the pH might drop a bit. But normally you have a high KH to prevent the pH from dropping too quickly or too far.

 

[aaronnorth]

I agree with Colin, it will only drop by about 0.2 max (if that)

FHM, i think he means the pH is high for aquatic plants

 

[kcharley]

Hi Spice,

I'm a newb when it comes to plants and have just one pressurized CO2 tank for experience.

Like you, I didn't expect the KH to drop with the addition of CO2, but mine did. Now my starting KH was a lot lower than yours, 3 vs 20. It went to zero and not surprisingly my PH dropped to 6.0 or lower. Even now that I've got the KH up to 5, my Ph is only 6.4. I don't have a clue how far the CO2 will drop yours.

I found an explanation on Barrreport.com as to why KH drops with pressurized CO2 but I don't remember the exact explanation. I think it has something to do with the carbonic acid neutralizing the KH but I really don't remember. If I can find it again, I will let you know.


HTH.

Greg

 

[Dave Spencer]

Adding CO2 does not affect the kH. The reaction is:

CO2 + H2O <=> H2CO3
H2CO3 <=> H+ + HCO3-

The pH changes because carbonic acid is formed.

Your kH test kit is actually measuring total alkalinity, not kH. Plant ferts could well be affecting this.

I run CO2 at 30ppm in very soft water with the pH down at 6 or so with no problems.

Dave.

 

[Colin_T]

Adding CO2 does not affect the kH.

Why do you say that Dave?
The CO2 is acidic and produces carbonic acid, as you mentioned. And the acids are neutralised by the dissolved carbonates (KH) in the water. Therefore the CO2 does affect the KH by using it up during the chemical conversion.

 

[Dave Spencer]

KH is defined as that portion of all calcium ions (Ca++) and magnesium ions (Mg++) ions present in water for which there exists an equivalent amount of hydrogen carbonate ions (HCO3–) and carbonate ions (CO3-–). It is very hard to find a correct description of this, as most FW forums have it wrong. As you can see, KH has nothing to do with addition of CO2 to water. Adding sodium bicarbonate doesn`t increase the KH like people seem to think.

H2CO3 <=> H+ + HCO3-

The total alkalinity is affected by H+ and HCO3-. From the above equation, there are equal amounts of H+ and HCO3-, so the akalinity is unaffected.

Total alkalinity = [HCO3-] + [OH-] - [H+]

If you are using a KH test kit with just one bottle, you are measuring total alkalinity, not KH. The total alkalinity is the buffering capacity of the water defined by its ability to neutralise H+ ions, and is not associated with the water carbonate hardness.

Dave.

 

[Spiceweasel69]

Cheers for the info peeps. Iv got a rock in there that must be limestone or something similar even though i was told it was aquatic safe.

I will install the co2 system and see what i get as a result. With the KH at 20, is 30ppm co2 still a realistic figure, and as aaronnorth says, how debilitating is a ph of 8 on aquatic plants?

Thanks in advance.

 

[Underwurlde]

pH of 8.0 I don't see any problems with that for plants.

KH is extemely difficult to measure (regardless of what your test kit is supposedly telling you) due to the problems mentioned above.

Andy

 

[aaronnorth]

there is some more information here ok kH:
http/www.fishforums.net/index.php?showto...274794&st=0

although most is similar to what Dave has wrote.

 

[kcharley]

Wow! I've read and re-read what Dave wrote four times now and the thread Aaron linked and all I can say is you guys are a lot smarter than me.

I understand that when I think I am testing Kh I may be testing something else. I understand that something other than CO2 may be causing my Kh to drop (in the absence of crushed coral in my filter.) I agree that plants may be perfectly fine with a "Kh" of zero. In fact, my plants were doing great with a Kh of zero and are doing very well with a Kh of 5. To the best of my knowledge, the only thing I changed when my"Kh" dropped to zero was to add crushed coral to the filter. Hmmm? I'm not sure my work addled mine can handle the addition of trying to understand the chemistry right now. So let me explain what I'm trying to achieve. Maybe I'm going after the wrong thing.

As a newb, I took it to heart when I read that a Ph swing of more than .2 would be fatal to fish. Now my tap water has a Ph of 8.4. So I became very concerned about doing water changes with tap water as the Ph of my tanks slowly dropped over time. So I went and bought RO water and calculated how much to mix with my tap to keep the tank Ph from moving more than .2. Even with that care, I was having occasional fish loss with water changes (I use Prime in measured amounts to treat new tap water) and I was being careful to keep the incoming water temp about 4 degrees less than the tank temp.

Then I started learning about total dissolved solids, Kh and Gh, and read some speculation that it wasn't a Ph swing that hurt fish but a total dissolved solids swing and particularly Kh swings. Note I recognized that it was speculation. Started testing for "Kh" and Gh and realized that my tank Kh had dropped to 0 and that I was putting in 3 Kh water. So I added crushed coral to my filters and my "Kh" in the non-CO2 tanks remains at either 3 or 4. I'm not sure it has stabilized yet in the CO2 tank but the change is gradual (I am becoming concerned though by adding lower Kh water to it.)

Interestingly, my occasional fish loss has stopped on water changes once I started matching the Kh of the incoming water to the existing water. I don't even try to match Ph anymore. I measure it out of curiosity and as an indication of what is happening to my "Kh". Anymore I find test results interesting (I don't even try to measure ppm on my CO2 tank) but I really go by are the fish and plants happy and minimal algae problems. If so, I don't worry about the tests too much.

If I'm missing something please let me know. I appreciate the education.