Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
If your tap water is pretty much OK, just too hard (high GH, KH, pH, TDS) then start with a blend of tap water and RO.
Get the GH and KH where you want it. Maybe 25% tap + 75% RO? Whatever works!
Then filter it though peat moss to get the black water, organic acids that many soft water fish like.