Very bad idea to change any water parameter in the tank, OK to run peat
in the tank to keep the water parameters stable, but do change
parameters before the water is in the tank. Changing the PH or Hardness
in the tank will also change the Osmosis rate of oxygen and nutrition
absorption.

I once had a tank that had a cloudy water problem that just would not go
away. I tried to adjust water parms, I did frequent water changes,
mechanical filtering, etc. Nothing worked. I finally got sick of it and just
left alone to rot and stink. Four or five days later it cleared up on it's
own and has been crystal clear ever since. Unless there is something dead
contaminating the tank, I just leave it alone and let it run.

I used to adjust the pH religously. Then I got busy and didn't have time to
mess with the tank. The fish didn't seem to care and remained happy and
healthy. My water is fairly soft and the fish seem to like it as is.