If you have a UV, you want to run it 24/7 or there is no point to the expense. Yes, they kill all bacteria that pass through it. You want it to kill all bacteria that pass through it. UV only affects organisms in the water column. The bacteria that you want in your tank is the bacteria that clings to the rock, the sand, to the biological filter media if any, to the glass surface, etc, etc. The bacteria in the water column will get zapped in the UV, which is what you want to have happen. In addition, a UV will help control cyanobacteria, which spreads by propagating in the water column. It will help to control a variety of non-desired algae blooms.
That last point means you will have to be diligent to feed algae-eating animals, such as most tangs, blennies, and inverts like crabs and shrimp.
But UV will NOT harm your beneficial bacteria. Period. It will help control bacterial and parasitic infections IF the flow rate is properly set through the UV sterilizer. You will have cleaner water, but hardly, hardly "sterile" water.
I am going to do my best to not respond if there are misinformed replies here. On another board someone got testy when I responded to information that was simply wildly off the mark on this issue. So this is my one contribution here to the subject. If someone wants to start a discussion, I'd request you start another thread on UV somewhere, and not further the matter in this thread on ick. But what I have stated is simply a fact, and if you are interested in UV, any search on any reliable source will reiterate the simple facts relayed above.
Oh, if you end up with corals, there is some dispute regarding the effect of UV on plankton. I have my own ideas on this subject, which is, you can have wildly propagating pods of all sorts, which to me indicates the same for most types of plankton if you get a population going, and UV will not substantially undermine that. You may well get some reduction, but not enough to kill the population off. But if FEEDING live plankton, it is a good idea to shut off the UV, and all pumps for that matter, for a good 10 minutes. You should do that though even without UV, so again, no difference with the addition of a UV.
Now, the "Cleaner Goby" is a cleaner goby. A "Cleaner Wrasse" is a cleaner wrasse. Just as the "Cleaner Shrimp" is the cleaner shrimp. These are the common names for each species. They each have many other names as well. But if you search on these you will find what you need. They will all help to control ick and other parasites as well.
If your clown fish has a bad case of ich, you have underlying problems, as those are among the sturdiest fish (being tank-raised and bred). So odds are you have temperature, salinity, pH, ammo, nitrite, nitrate problems in there somewhere. Some combination of these, and they are rank ordered in terms of likelihood for your testing convenience. So adding anything is out of the question until you deal with whatever has caused this outbreak. Even UV will only be of limited help. You need to get your water situation figured out. It is not uncommon at all for Tang to get ick. But for clown fish, that is a signal of something not good.
You need to get good tests of all these parameters. Would be interesting to see what they are if you can post.
That last point means you will have to be diligent to feed algae-eating animals, such as most tangs, blennies, and inverts like crabs and shrimp.
But UV will NOT harm your beneficial bacteria. Period. It will help control bacterial and parasitic infections IF the flow rate is properly set through the UV sterilizer. You will have cleaner water, but hardly, hardly "sterile" water.
I am going to do my best to not respond if there are misinformed replies here. On another board someone got testy when I responded to information that was simply wildly off the mark on this issue. So this is my one contribution here to the subject. If someone wants to start a discussion, I'd request you start another thread on UV somewhere, and not further the matter in this thread on ick. But what I have stated is simply a fact, and if you are interested in UV, any search on any reliable source will reiterate the simple facts relayed above.
Oh, if you end up with corals, there is some dispute regarding the effect of UV on plankton. I have my own ideas on this subject, which is, you can have wildly propagating pods of all sorts, which to me indicates the same for most types of plankton if you get a population going, and UV will not substantially undermine that. You may well get some reduction, but not enough to kill the population off. But if FEEDING live plankton, it is a good idea to shut off the UV, and all pumps for that matter, for a good 10 minutes. You should do that though even without UV, so again, no difference with the addition of a UV.
Now, the "Cleaner Goby" is a cleaner goby. A "Cleaner Wrasse" is a cleaner wrasse. Just as the "Cleaner Shrimp" is the cleaner shrimp. These are the common names for each species. They each have many other names as well. But if you search on these you will find what you need. They will all help to control ick and other parasites as well.
If your clown fish has a bad case of ich, you have underlying problems, as those are among the sturdiest fish (being tank-raised and bred). So odds are you have temperature, salinity, pH, ammo, nitrite, nitrate problems in there somewhere. Some combination of these, and they are rank ordered in terms of likelihood for your testing convenience. So adding anything is out of the question until you deal with whatever has caused this outbreak. Even UV will only be of limited help. You need to get your water situation figured out. It is not uncommon at all for Tang to get ick. But for clown fish, that is a signal of something not good.
You need to get good tests of all these parameters. Would be interesting to see what they are if you can post.
Thank you so much for your information. 
I got a uv sterilizer today, and I am so pumped 'cause my 
Duh?! 
