Why wont my new goldfish eat?

Yesterday I added two goldfish to a 25gallon tank. The tank had previously been used for tropical fish so the water had the right balance of bacteria and what not in. I've checked the water for ammonia, nitrates etc etc and all is good, the fish just don't seem hungry. They take no interest in the floating flakes and they will munch perhaps one pellet from the bottom of the tank and leave the rest. Any suggestions?