I feed different foods and at different intervals.
My piranhas I feed sometimes 2-3 times a week or sometimes I make them go 5-6 days without feeding. I have an African cichlid (M. chipokae) in with them so he goes without also.
Cichlids I feed once a day most of the time but a couple times a week I'll feed twice but they go without food one day a week. Same schedule for my redtail black shark and my feeder fish.
I have different foods I rotate from. Krill, shrimp, earthworms, live fish, brine shrimp, veggie flakes, cichlid flakes, spirulina flakes, spirulina tabs,3 different types of pellets, bloodworms, a few others I can't think of right now. I also feed mice to my piranhas on occasion.