Running UV will not kill the beneficial bacteria as most are stating here - this is a running myth that has been passed on from person to person with no real data (that i have seen atleast - and i spend a lot of time online
).
lets look at some examples;
1. in reef tanks you can easily do 50%-100% water changes without heavily impacting the bio filtration the system is capable of. Why is this? Because the MAJORITY of the beneficial bacteria are housed in your sand bed and on your rock NOT in the water column.
2. when you want to see new rock you dont use old tank water (though it helps somewhat), you use a piece of ESTABLISHED live rock because it contains the majority of the bacteria you want in your system.
3. multi million dollar aquariums USE giant UV sterilizers with no issues and their bio loads - this includes reef systems, not just fowlers.
4. the water running through the uv filter should be mechanically filtered first or you will clog up the system and reduce the efficiency of the system. Pods shouldnt make it through mechanical filtration if you are doing it right. you want to use the UV to kill algae spores and water borne bacteria. Also - skimmers also pull pods out of the tank and nobody seems to be removing those off their systems.
5. is there any proof of a tank crash or algae bloom from running UV? (if the uv was killing beneficial bacteria then your phosphates and nitrates would jump feeding such a bloom or killing fish and corals)
6. lots of people run UV and are just as successful as those that don't. Its an extra layer of protection. If you are going to use it get a good system (like the Emperor Aquatics units) and get a Tom's Flow meter and make sure you are running the correct flow through the unit to optimize the filtration.