I have a red brittle about a foot long from side to side, stretched out. I just put some flake food next to him and he ran away from the place. i thought he would soak up the food with his tentacles?
i have know brittle stars to be meaty eaters, you could try adding something meaty that comes frozen and will once thawed sink to the sand bed, a friend of mine had one eat 3 healthy fish that were not so lucky so anything with meat it may accept, you could also try asking the place you got it from what they used to feed it
they seem to clumsy and slow for a fish. Fishes are like lightning. I can see perhaps at night while the fish sleeps, but even then, the clumbsy arm of a brittle would seem to wake a fish with enough time to escape.
Larger Brittle stars will sometimes "jump" ontop of a slow moving fish. And also they prefer meat, which includes fish like silversides, tubifex worms, blood worms, and shrimp pellits.