It seems that several fish species change their diet habits as they mature, especially angels and tangs. It may be a actual diet need trying to supplement something they need to mature or could be they just wanted to try something different. It’s in their nature to graze for food constantly even when full so some people speculate that if you feed them several times a day it helps keep them from starting on things you want t keep in the tank. What’s worse is fish learn from others on what to eat. Tri and Marc both experienced this with hippos eating zoa’s and then teaching others.
