I've used a UV for years on my tank and wouldn't run without one. I think they keep your stock healthier and they'll polish water to a very nice clarity. You have to size them according to your flow rate and what you want to accomplish - algae control, bacteria control, etc. I'm currently using a Classic Series Aqua UV. It's a much more well made unit than the popular Turbo Twist by Coralife. A lot of people are going to tell you they're a waste of money and you don't need them but most, not all, of those people have never used one. Here's a link for Aqua UV with a lot of good info.