It depends on your method of reefkeeping, While it will kill off all Ich and bacteria and phytoplankton there are critters that eat that stuff, not just cleaner shrimp but sponges and tube worms and scalops and corals and tunicates, same goes with protein skimmers and water polishers, if you have an outbreak then yes ou want to use UV to help em get over it, claner wrasses and skunk cleaner shrimp are great additions too, and good long term help aswell, the best way to keep deseas out of your tank is to behave well with new additions and to keep your fish happy and healthy.