The one I lost was eating pellets, frozen mysis, and a whole host of other things. The biota mandarins are really awesome.After getting Mandarin to eat, its a real drag to loose one. My systems are large with vegetable filters with copepods & amphipods. Do you grow other live food besides brine shrimp.
I had moved some stuff around and introduced some new fish and there was some chasing going on - and one of the openings in the screen cover was just a little big.
We've got another mandarin in the other tank - and he also eats pretty much everything - and mostly has since day 1. Biota does a pretty awesome job with them.