I have used tap water for the entire 10 months my tank has been going. Everything has been doing well. Had one hair algae bloom but got that under control pretty quick. I would say give it a try and see how it goes. I keep mainly z's and p's, but my LPS are doing well also. Very limited sps, but those are ok also. Just some digi, monti, and spongeodes but all 3 are doing very well. Don't think it would hurt at all to cycle with tap then slowly switch to RO with water changes and top offs. I'm a noob though and still learning, but I have had no problems with using tap for 10-11 months.