Well there's different opinions about uv's some like them some think there a waste of money. I have one myself and I think if you can afford one they can't hurt they can only help. They are suppose to help with water clarity and algae. One thing though a good uv will cost you more then an ro/di unit, if you had to pick one or the other I would go with the ro/di unit. you could always add the uv at a later date. By the way how big is the tank. You can get a ro for around $150 a good uv like aqua ultraviolet would cost more then $200