A) Your fish don't grow, for the most part, because you feed them more or less (except maybe for fat or skinny). But young, small fish do 'seem' to get bigger quickly.
B) You should never feed more than the fish will eat with in a few minutes after you have put the food in the water. For clowns, once a day is good, if you feed twice a day, make sure all the food is eaten very quickly, and feeding every other day is OK if the fish are not very young, very small, underweight (skinny) or unhealthy.