Filter and heater could be as same as an UV, optional item, or requirement item, depend on how you keep your tank, and what you keep in your tank. Back home,we kept fish with daily water change, and without a single filter. I've unplugged my heater on some tanks since February, and have some tank that haven't had a heater for year
Water could also be considered optional depending on what you want to keep......
I agree that a uv isn't necessary, but for certain fish I would use one (if ever I keep another group of clown loaches I'll be running one).
Sent from my HTC Desire HD A9191 using MonsterAquariaNetwork App