Which UV for my tank?

So all but one fish in my tank just died within a couple of days of each other. One of the dead fish have been in the tank for a couple of months. Only fish left living is my foxface so im thinking some kind of parasite/disease. Well this ordeal has convinced me to get a UV Sterilizer. Now my tank is 55gallon with some liverock, hermit crabs star fish, and some snails. So which UV to get?

 

What makes you think UV sterilizer? In fact I can think of alot of things but a UV sterilizer isnt even on the list. In fact a UV sterilizer is far from necessary, I mean I dont run one & probably dont ever plan to. Please provide some more information. symptoms, full tank description, livestock, feeding amounts & times, filtration, substrate, live rock, water params, even pictures if possible. I mean live EVERYTHING. Cause I really dont think a UV is part of the big picture solution.