Hey Clutterydrawer
I've used peat as a bottem cover for killies, and am now using it for a couple pair of bettas.
For the bettas I just use enough to cover the glass bottem . For the killies I used more.
My water is well water , about 7.5 to 8 , probably hard. I don't find that the peat changes the PH very much.
I really believe the peat imparts some medicinal (?) , quality to the water.
I've never used it with a strong filter , just an airstone or inside filter. It gets stired up sometimes , but it looks natural , and the fish do well in it.
Most Important........put the peat ( the fine powdered kind, not spangham moss), in a clean bucket, then fill with water. let it soak until all the peat sinks to the bottem , Usuallythe better part of a week. You may want to pour some of the brown water off and resoak.........Then......put in the aquarium.
Luck with your fish
KF