Help! I think i gassed my fish

[Mebbid]

Whats your dkh?
How big is your tank?
How big of a water change did you do?

 

[beeritself]

Unsure of dkh. 55 gallon. 50% water change.

 

[Mebbid]

Unsure of dkh. 55 gallon. 50% water change.

Without knowing your dKH telling us the pH reading really isn't helping at all. You have to know both the dKH and the pH to get an estimated reading.

The only real thing that makes me think that it's the co2 over the water change is that you did another large water change. If the water change is what hurt the fish then it would stand to reason that a second water change in short succession would have been the final nail in the coffin.

Depending on how fast you're putting co2 in the tank it could have potentially built up very quickly and even been made worse if there is a high level of co2 in the tap water which does happen in some cases.

I would suggest getting a quality dKH test, and even a digital pH probe that can be run constantly. Combine that with a drop checker and you should be able to have a good idea on how your co2 levels are at any given point.