I feed mine silversides, krill, and mysis, about twice every three weeks. If I'm feeling ambitious, I'll sometimes soak the food in selcon first. BTAs also get nutrition from the water column and your lighting, so the frequency of feeding at some point really is a matter of how big you want it to get and whether you want it to split. When feeding silversides, though, make sure the pieces are on the small size... most people say no bigger than 1/4", but I go up to 1/2". The BTA will go ahead and swallow whatever it can, but if the food is on the large size it will often reguritate the mass a few hours later, often when your lights are out, and then you'll be left wondering why your water parameters keep getting worse and worse.