PH change due to CO2?

[current516]

I just read in another post something that surprised me. It seems like the more I learn about this hobby the less I know. Anyway...

I read that PH change due to CO2 does not harm fish. Only PH changes due to KH would harm them. Am I understanding this correctly?

I thought that If the CO2 levels got really high they could cause your PH to crash, especially with low KH. But why would we worry about that if it doesn't harm your fish? Do high CO2 levels change your KH too?

Let's say I want to keep Discus (I do eventually). I'm supposed to have a "stable" PH. Does that not include changes due to CO2 injection?

Thanks

 

[KhanJee]

PH changes due to CO2 is correct. In day and night time PH readings are always different because of CO2 and its normal.

I never experienced KH change due to CO2. If you have lower KH and a lot of CO2 then water will become very light.

What it will affect on your fish depends on what you are stocking. In your case all fish which love light water will be happy.

For discuss you need light water.

 

[Purrbox]

You're correct that pH changes as a result of CO2 do not harm fish.

The fear that CO2 can cause a pH crash has to do with a tank with a low KH (<3dKH). There have been several people running tanks with a low KH (softwater tanks for difficult plants) and good CO2 levels that have found this to be less of a problem than originally suspected. It still helps to keep the KH up as it makes it easier to determine your CO2 levels as the pH can become unreadable to most pH test kits otherwise.

Because you are dealing with CO2 injection, you should revise it to being a stable KH instead of a stable pH.

 

[current516]

Thanks all! OK. So...

My PH is usually 6.8-7.2 and my KH ranges from 8.5-9.5

I plan on getting some Discus. Let's say they need a maximum PH of 6.4 and a maximum KH of 5 (These #s are arbitrary! I haven't done my research yet).

I was thinking of getting a PH controller to keep my Ph at the 6.4 #. But that wouldn't do any good for the discus right? Because that's only changing the PH through the use of CO2. Does that mean the only reason to have a PH controller is if you have really low KH?

So for Discus, it would be more important for me to address my KH. Using RO water or something to get it down to the right level, whatever that is. That should change my Ph levels too, right?

Am I understanding this correctly?

 

[Purrbox]

You'll want to stabilize your KH. This may or may not need to be lower than what you currently have, I don't know a lot about Discus. RO water that is reconstituted to the specific parameters that you need would be the easiest way to achieve this, and I would expect to be recommended for more delicate fish like Discus. Whatever KH you set your tank at will have a base pH associated with it, the CO2 will then push the pH about 1ppm lower.

The PH controller is beneficial to help you keep your tank at a specific CO2 level and will minimize CO2 waste. This is beneficial reguardless of you KH level, but not strictly necessary.