I will add that my water is very soft (PH 6, hardness of 3). I run crushed coral in the filters and use coral rocks and/or argonite sand to raise the hardness of my water for fish that need it (CA cichlids, goldfish tank)
Never have, never will. If you have to lower pH, use peat or driftwood, and if you need to raise it, use crushed coral sand. Buffer isn't great for the fish themselves.