co2 and ph fluctuations

[DocB]

As I research more into co2 I discovered adding a pressurized co2 system will lower ph. I dunno how much. a couple of tenths?
I have a 55 gal tank with water at about 7.7.
If the co2 process lowers it, then every time I add aged water it will raise it. Will this fluctuation stress the discus?

[darbex]

Co2 will lower your pH. How much will depend upon your taps KH reading for example my tap water is 7.8 pH with a KH of 8.0. To get my CO2 level in the "green" zone my pH needs to be about 6.8 - 7.0 after CO2 injection. But lets say that your KH is only 2.0 then you would need to drop your pH to 6.4 - 6.6. Now if you are doing large water changes then yes this will significantly change the pH. However, in a heavily planted tank you dont need to do large water changes as the plants will filter alot of the nitrates out. I have a planted tank that I have not changed the water in a year only top-off but I also dont have Discus in this tank so dont know how they would take that.

[DocB]

Wow I didn't realize it would change that much.
I do weekly WC of about 50%+
I am not as concerned with the beginning or ending Ph as much as how the Ph drop on WC day would affect the Discus.

[Chad Hughes]

Large water changes that influence to Ph will not typically harm discus. I only change water in planted tanks once every week or so and those water chnages are large (50% ++). The Ph does swing and the CO2 slowly bring it back down. Ph swings from low to high are typically tolerable. It's the high to low swings that discus are very sensitive to.

Hope that helps!

[darbex]

+1 I agree with Chad that raising the pH has less of an effect on fish than the drop. You may want to do 20-30% every few days since even raising the pH to much will still stress them. just a suggestion

[ChloroPhil]

Don't forget that you're not changing all of the water so you're only going to modify pH by a percentage difference rather than the full deal. Also, the change isn't immediate so the fish have some time to adjust as the new water is added to the current volume. Even doing large WC with very low KH water I didn't measure a large change in pH on my pH meter.

Regards,
Phil

[Chad Hughes]

I have pretty hard water so my shift is significant. Ph meter typically reads about 6.8 before the change and 7.9 after. That's quite a bit. Still no ill effects.

Best wishes!

[DocB]

I have pretty hard water so my shift is significant. Ph meter typically reads about 6.8 before the change and 7.9 after. That's quite a bit. Still no ill effects.

Best wishes!

That is pretty significant!
My water is about 7.9 now - I don't know how much CO2 will lower it but I assume it would be within your range.
That's encouraging.
Now on to find a system...

[Sharkbait]

Wow Chad! That's quite a shift!

We're very lucky here on the island to have soft water. My PH shifts are very minimal with my C02 and water changes (6.4-6.5, maaaaybe 6.6).