The fact that is most largely ignored about UV's is that they dont PREVENT anything. Ich, free floating algae and bacteria still exist in tanks that run a UV. In 9 years and just as many tanks ive never had a situation that needed a UV. Parasites, free floating algae and bacteria can be dealt with in more effective ways then spending the money on a UV that wont cure anything.
UV's only deal with the organisms that pass through them, and the flow rates are far too slow. What this means is that never will the tank be 100% sterilized, not even close.