You can check your tap KH
. It is probably high.
The best way to deal with it is to keep fish that like high PH/KH/GH
. Cichlids like that.
Usually that's a thing you must check before you put the fish in the tank, but now it's too late.
Tetras like cardinals like low KH
values and acidic ph. A way to not use chemicals is to use reverse osmosis water for water changes
. It will result to progressively lower your KH
values then PH will progressively drop with WCs.
If you don't want to buy reverse osmosis water for each water change, you can buy a reverse osmoser
to your tank, but that's a bit expensive.
You can go low cost chemical solution, use ph down
, but this is very strong acid, and it can stress fish a lot if not used properly. But I think if you use PH down, it will raise by the time anyway because of the high KH