A lot of folks insist on RO water when you have a well. IMO&IME: in a fish-only tank, you can use most well water with no problem. Iron ( and lots of other heavy metals, etc) is easily removed using a resin, like Chemi-Pure. Also, be sure to test for copper (more of a problem than iron), phosphate, nitrates, phosphates, and anything else you can. You even might think about getting a professional water analysis.