Originally Posted by Dmaaaaax

What is the pH of the water before adding it to the tank? You have to know how much the pH changes with each water change. This is what will affect the fish. For instance I add water that is at pH 7.0-7.2, the CO2 drops that pH down to around 6.5 or lower daily. My CO2 is off at night, but yours will be constantly on, so you want to watch that it does not drop too much.

If you are using just RO/DI water then your hardness is probably around ~1-2, which is low.