Having a UV Sterilizer on a tank holding Ich-prone fish like the Hippo Tang is a good idea. A UV Sterilizer interrupts the life cycle of Ich, but the life cycle can be anywhere from about 24-72 days (temperature dependent among of things). Since this is such a long time, a UV Sterilizer is not a good
treatment, though it is a good
preventive.
As long as the fish is active and eating the tank transfer method is a good option, but if the fish is not in good condition TT, like UV sterilizer, can take too long and the fish may perish. For me, it's about common sense; if the fish is covered in Ich, then treatment with a medication is often the best bet. If the fish has a mild case, then TT may be the best bet.
In regards to your other comments, is this your first reef tank? For a tank that's only 6 weeks old, you have a lot of fish in there already. IMO, you're probably moving a bit too fast. Did you use 100% live rock or did you use dry rock too? Dry rock is not equal to live rock. What brand of test kits are you using to test the tank? Are you using a refractometer or hydrometer for testing salinity? What are the actual numbers you've tested? "Parameters are good" is a bit vague. Just trying to make sure you're on the right track, regardless of the Hippo Tang situation.
