There are different flow rates needed to kill different things with a UV light. The UV will not add too much heat. The more watts, the more water you can pass through quicker and still be effective.
As for the fish, Matt, that is irresponsible. You say you have plans to upgrade tanks. If you knew you were upgrading, why not just wait? Just because it's small now, doesn't mean it still doesn't need space. These are fish from the ocean and are used to having all the room in the world. You already have clowns and chromis in that tank, why not another small fish? I have a 75 gallon and would love a Powder Blue or Regal Tang, but a 12" fish would not be happy in my tank as it's only 4ft wide and the fish would be turning around every few seconds. I'd like to get a smaller tang, maybe a Powder Brown, but only if I upgrade to a 90 gallon tank this summer. I am planning on a 140-185 gallon tank in the spare room when one of my roommates moves out in May, and I could have a whole host of fish, but I will wait until the tank is ready to get them.
It just seems like, for all the research you have done for your tank, you listened to your own selfish desires, not what's best for the fish. The fact that the first thing you said was, "Before I get shouted at, my mate at the
LFS said it would be okay" is an indication that you knew what you were doing was wrong, but didn't care. Stores are in business to make money, and with the world economy in the shape that it is, stores that sell luxury items (and yes, $60 reef fish are luxury items) are hurting as people are cutting back. It may not have been on purpose, but your friend is wrong in this issue.
Do you know how much larger tanks cost to maintain? It is a large investment, both time and money. Are you prepared to drop $800 for this fish within the next year for a proper home (which doesn't even have to be a reef but a FO setup)? If not, take him back now as he will get very stressed and die in that tank, and you'll come back here and say "I don't know what happened, he was healthy". For starters, the best way to cure ich in a fish like that is not in a QT tank, but to leave the lights off, feed plenty of food, and make it as happy as possible, no medication.
And matt...please, please, please, please, please, please clean the tank before shooting video...
