low level review...

I used San Antonio tap for a year or two when I first started the hobby and ALWAYS had algae issues and difficulty keeping SPS (could obviously be because I was new), but when I switched to RO/DI, the algae problems left and SPS began to look purdy.

I guess for me, using RO/DI just rules out one source if things go bad or it at least limits the possibility of some potential problems. I can think of several people that have successfully used tap water on a reef....but they also had a few battles and they had to keep a strict water change schedule.