I've used RO only in my planted tanks and my cichlid tanks and I've never had a problem with it. You can ask 10 different people this question and you'll get 10 different answers. I don't think you'd have issues using RO as your top off, as its only there to replace the H2O that has evaporated. The minerals and whatever will still be in the tank. Water changes is a different story but like I said, I've been doing it for years and never had problems. Good luck
PS. Check into the large bladder tanks that hold the RO. You can use that with a solenoid and float valve so that the water will be stored in the bladder until your tank needs it. Keeps the RO from running indefinitely.
PS. Check into the large bladder tanks that hold the RO. You can use that with a solenoid and float valve so that the water will be stored in the bladder until your tank needs it. Keeps the RO from running indefinitely.