UV sterilizer

[BCOrchidGuy]

UV sterilizers kill organics that pass through them as long as they are moving slow enough to be killed, if you use a powerhead that forces the water through to fast for the critters to get a fatal exposure to UV light they won't all be killed.

As Brad says, it's not selective though, good as well as bad gets done in. If you have a hospital tank with a sick fish, UV is great, in a reef that's well maintained I wouldn't bother with one, again like Brad says, Skimmer .

Doug