I started keeping fowlr tanks 35 years ago. I hate to tell everyone (hung up on 0 tds) but there was no such thing as rodi water. I used what I had, I later found out my in was about 300 tds. I seldom had any problems. I do have a good rodi system now but it will only stay at zero for a few weeks.then goes up to 10 or so. I'm not worrying about it. I have a few soft corals and mostly fish. Maybe it makes a big difference with difficult corals.