I have two tanks which I would like to move fish between. I use treated
tapwater for water changes in both. My tapwater has a KH of around 5, but
problem is I am injecting CO2 into one of the tanks which drives the pH to
around 6.8. pH in the non-injected tank is around 7.6. How can I lower
the pH/KH in the non-injected tank to make the parameters closer? Do I
need to use distilled water and mix to the desired KH, or is there a good
buffer that will hold around 6.8-7?

TIA,
Ben

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