Not normally.  Based on the amount of flow for a UV sterilizer and the size of your tank it may totally destroy the beneficial bacteria in your tank.  This bacteria is what converts the Ammonia created by fish waste and rotting food and plants into Nitrites and Nitrates.  A UV sterilizer could completely remove all of these.  However, they can also kill many of the disease causing bacteria found in a tank.  Typically these are better used in Salt tanks rather than Fresh tanks.  Additionally they should normally not be used at all times rather as a suplement when illness strikes your fish to help stop reinfection and spreading to other fish.  Typically if you are medicating fish it normally kills most of the Biological filter (bacteria) anyway so using a UV sterilizer will not really hurt things any worse then.  This will ensure everything is dead prior to you recycling the tank.  Recycling will be explained in another FAQ.