That perc really should be getting a more-varied diet for optimal nutrition. If nothing else, he's likely to have his colors fade unless he gets more than mysis. You might consider adding krill, Formula1, and/or a few other things to round out the diet. Bob Fenner has a nice recipe for a cheap, easy, nutritious make-at-home fish food in The Conscientious Marine Aquarist if you have access to a copy of that book.