A UV will kill bacteria, but first it will kill free floating algea, then free floating bacteria but it would require a longer hang time, and then finally parisites, and thats the tricky part getting the water to stay in there long enough to kill the parisites and then once again it is only the free floating parisites, not the ones on the fish or that are in the substrate.
Much of what you desire in your sandbed and on your rocks for critters will breed in your water colum, don't kill em by sticking them through UV lights.
Thomas