What are your TDS readings?

Read TDS of your top off fresh water. For a reef, should be zero. For a well established FOWLR tank, it can be higher - though most will suggest keeping it as low as possible.
Trying to read TDS in saltwater will really jack up your probe.
 
I used tap water with a TDS reading of 55 ppm to fill my new tank. I was planning to use RO/DI for top off and water changes going forward. Any potential issues?
 
I use/have used dechlorinated tap water in many marine systems over the years.
You may have a little algae at first if anything (depending on your source water), but nothing too bad for the fish.
 
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