Depending on the clowns they grow to different sizes and they will max out according to the available swim space as well. Often marine fish never get the size they would in the wild as the space in our tanks is just too restrictive. A 55 gallon tank will have about 35 to 40 gallons of water when you take the displacement of water due to sand, rocks, and other items we place in the tank. Using seven to ten gallons of water per fish as a rule of thumb in a salt water tank for fish that are about two to three inches in length then you have the correct length for the fish.
Feeding the clowns, they do eat dried algae, protein pellets and frozen foods like brine shrimp. A variety is best for all fish, and the clowns will enjoy the variety as well.