Before others disagree(especially the ones that quarantine everything and swear haven't had ick for 5,10,20 years..), I will tell you what happened in my tank, and you take your own conclusions. I have a 24W running from the outflow of a small canister filter, that has a bag of chemi-pure in my 20 gal reef. The flow that comes out of the canister and through the uv is less than 90 gal/hour. I had an initial outbreak of ick 2 months ago. Quarantining the fish after its got ick is extremely hard, since the catching some fish in a reef is practically impossible. After I got the UV, I kept the fish in the tank and tried to minimize all stressing factors that could worsen the problem and allow the disease to settle in for good. I tried feeding them live brine shrimp more often, so they would keep their appetite and immune system up. Made sure my water parameters were in check. Ran my uv 24/7. Slowly the fish recovered, and I noticed less and less spots, and today I do not see any signs from it. It has been 1.5 months since. If you understand ick's cycle, you know that there is a swimming stage. At that point you have a chance at killing, in a couple of hours(assuming you can run your water volume through your uv efficiently, at least 2x in an hour) most of the creeps swimming in your tank. I KNOW YOU WILL NOT ERADICATE ICK WITH UV, however you will be able to help your fish bounce the disease on their own while you keep them from completely blooming in your tank.
After I understood that the parasite will be present in your tank sooner or later, you CAN help the system by having a UV. Having the DISEASE is another thing, linked to stress, lack of nutrition, poor water parameters. You can have the parasite in your tank, but not allow the disease to get into your fish.
The issue with so many against Uv's is because they do not have efficient units, that are used properly, and therefore do not do work on preventing or even killing algae. At the same time, we see companies making lots of money making these 8,9Watt versions that do not by any means are strong enough to kill the parasite. If you are serious about helping kill parasites, get at least a 18W, and run it with a 50-100max gal/hr flow. You will see clearer water and find the equipment to work for you.