Question about PH (+KH/CO2)

[Choco]

I alway read about how some fish/shrimp want a certain PH value and stable PH...etc
However, reading some more about aquarium stuffs...PH value is really dependent on KH & Co2 Level..

Then I also found out from many people that, PH change due to change in Co2 level does not affect fish..

So doesn't this mean PH level really doesn't matter at all, and all the fish/shrimp cares about is only the KH level?

If so, why are we alway talking about water PH, and why most people test for PH instead of KH? (since PH can really "lie" about what the fish really want if it is KH they care about)

 

[loaches r cool]

IDK why people fuss so much about pH, many dont. The usual advice given for the average fish is to do frequent water changes so your tank doesnt stray to far from your tap, whatever that is, so long as its within reason.

pH is a result of many things, not a cause for the most part. If you pH suddenly changed and your fish died, then folks say the rapid change it pH killed their fish. But its probably not the pH, it is what caused the pH to change. I'd wager that TDS is more important than pH, though very few actually test it despite it being fairly cheap tester.

CO2 does not effect water hardness, TDS, KH, etc., so it is not harmfull to fish other than actually having to much CO2 in thier blood. So far in my 240G I get a full point pH swing due to running 30ppm during the day and shutting of overnight. So far the only fish that have died are a couple Ottos, but those seem to have a high drop off rate the first month or two anyhow.

 

[yourchoice]

For basic fishkeeping if the Ph is stable The Kh is right around where you want it to be.

 

[Mgamer20o0]

its hard to explain but the change with co2 isnt really changing the ph.

 

[Canuck]

My biggest beef with pH is that it tempts many, especially beginners, to try to adjust things they should leave alone. The pH of water can still be important for a couple of reasons. In a cycling tank or any tank where ammonia is present, the ammonia is much more dangerous to fish when the pH is over 7. Normally in a well established tank with a reasonable bioload, this isn't a concern, but one should be aware of their pH and able to take appropriate action. Of course taking appropriate action means using an ammonia locking chemical NOT adjusting pH. The second reason as alluded to earlier, a changing pH should be a cause for concern. A pH that declines means that acid production in the tank is higher then the current water change regimen is able to deal with. This decline can also signal increasing amounts of DOC, falling hardness and a bio filter that is becoming overwhelmed. These are the symptons of OTS and spell trouble. I agree with you that kH test kits should be used much more to help determine problems. I think pH kits are important, the problem lies in that many don't understand what the pH means.

Mgamer said "its hard to explain but the change with co2 isnt really changing the ph."

I'm not sure what this means. PH measures the ratio of negatively and positively charged hydrogen ions. While present, additionaly CO2 changes this ratio by increasing the amount of acid (carbonic) in the water. This change isn't permanent and doesn't affect hardness values but the pH has changed. Maybe you could explain further?

 

[loaches r cool]

I think he is just saying a round about way that fish dont sense the change of pH due to CO2, even though the pH does change, the fish cant tell it. All the rest of the water parameters, TDS, etc. that can cause osmotic shock and the fish can sense are the same as they were with the starting pH value before CO2 was added.

Something I have always wondered though, can hardness change via CO2 injection? For example I have an aragonite substrate tank with plants that I had though about co2. If I add CO2 to this tank will it begin to dissolve some of the aragonite due to the increase in acidity? If so then I'd imagine calcium and such would cause an increase in GH and TDS. Or is it simply not a strong enough acid to do this? Any thoughts?

 

[H3D]

CO2 does affect the pH! C02 forms H2CO3 (carbonic acid) in water. If the KH is too low it will drastically lower the pH. The key to preventing CO2 from altering the pH is making sure the water is properly buffered (proper KH level). A pH change will/does effect the fish. Some fish will tolerate a lower pH and are OK, but some fish will not!

Most people do not test for KH because most do not use CO2 and proper water changes will replenish this buffer. I would strongly advise any one who uses large amounts of CO2 and/or doesn't do frequent large water changes to monitor their KH with a test kit.

 

[H3D]

Something I have always wondered though, can hardness change via CO2 injection? For example I have an aragonite substrate tank with plants that I had though about co2. If I add CO2 to this tank will it begin to dissolve some of the aragonite due to the increase in acidity? If so then I'd imagine calcium and such would cause an increase in GH and TDS. Or is it simply not a strong enough acid to do this? Any thoughts?

It would depend on the type and "total" water hardness.

 

[loaches r cool]

The key to preventing CO2 from altering the pH is making sure the water is properly buffered (proper KH level).

CO2 will alter pH and for normal ranges of KH there wont be much (if any?) difference in how much the pH swings. Unless your using RO water, or have fish that actually prefer hard water, I'd not worry about keeping a higher KH. The pH swing from going from 3ppm co2 (ambient) to 30ppm co2 will be about a 1 point swing in pH, regardless wether your KH is 1 or 10. All KH does is skew the pH upwards. On TPT we are having this same discussion right now too. This seems to be a myth that wont die...

 

[H3D]

CO2 will alter pH and for normal ranges of KH there wont be much (if any?) difference in how much the pH swings. Unless your using RO water, or have fish that actually prefer hard water, I'd not worry about keeping a higher KH. The pH swing from going from 3ppm co2 (ambient) to 30ppm co2 will be about a 1 point swing in pH, regardless wether your KH is 1 or 10. All KH does is skew the pH upwards. On TPT we are having this same discussion right now too. This seems to be a myth that wont die...

No one said to keep a higher KH. I said to keep a proper KH. Agreed the pH may only fall by 1 point but that is a dramatic enough change to kill a fish if it happens too fast. Even that assumes keeping a proper water change schedule to remove acids from the tank and replenish the buffer.