If you are using a reverse osmosis system for your tank water, is it still necessary to use Prime? If not, is it advisable?
Well, you will need to for a FW tank, or your tank will eventually suffer a pH crash. There is nothing wrong with well water for FW fish. What is the pH, ammonia, nitrites, nitrates, GH/KH on your well water, and for that matter, on your tank?
The well water has minerals needed to buffer and maintain pH, that get used up in a FW tank. Pure RO will slowly cause your pH crash. Some folks use RO to mix with well/tap water to cut it if it has certain extremely high issues in some areas.
Do you have a good liquid test kit to test your tank water?