depends on what you want from your discus and what type. if you are looking to breed wilds then yes, you'll need to go with RO. many domestics are raised and bred in high ph. my wilds are in a steady 7.6 ph and are doing great, but it's a show tank and I realize that even if they lay eggs they would not hatch. using RO will work but be careful. a steady high ph is much better and easier on your fish then a changing ph.