In the wild fish don't live in a sterile environment. They are exposed to diseases and bacterias of all sorts all the time. Fish not exposed to a natural reef environment have a weak immune system, since they have not built there immune system up. All sorts of beneficial bacteria are killed off too. If you have problems with algae a UV sterilizer is not going to be the best solution. There is most likely something wrong with your water chemistry (high nitrates, high phospates). Bottom line a UV sterilizer is not neccesary.