Vincent, return them both. I have a 3 inch juvenile clown tang in my 6 foot 150 but am upgrading to a 400 gallon tank in the Spring. They do tend to get mean, but not always. He is currently with one other tang, a Yellow, and my Yellow is the meanest SOB I've ever seen.
My Clown tang started eating brine in the LFS first, but would not take Mysis. It seems many fish will eat Bloodworms readily, so I gave him that and he started eating right away. Now he'll eat Bloodworms, Mysis, and Nori but never even looks at pellet food. In the long run, unless you are upgrading to a tank at least 4 times the volume it's no good to keep it. This fish has a hard time in qt and can wither away very fast. It's one of those fish that can look great and just drop dead. Mine seems to only eat food when it's moving in the current. You could try putting the food in front of the powerhead to see if he chases it.
Unless you keep perfect, unpolluted reef parameters with high ph, EXTREME flow, high salinity (1.026) and oxygen at saturation you're not ready to try this fish. If you don't know what these terms mean....you're definitely not ready. I'm not trying to be hard on you...just stating the facts. I waited a long time for my LFS to bring in a good one. I have a good relationship with the owner and asked that it be placed in their 125 gallon reef tank...not a small, copper medicated tank. I put a deposit on the fish and stopped by every other day for a few weeks to watch it eat and see what it was eating and picking at. These tangs in particular are known to have a specific bacteria in their gut that copper can destroy. Even if they're eating well, they'll always appear a bit thin and just die if this bacteria is killed. They're very touchy, and really not a fish for you right now.
Please take them back.
