IME,its perfectly normal for BTA's to retract/expand during the course of a day/night.I wouldn't worry too much about it right now.Since you've only had it for a couple weeks,its still getting used to its new environment.For your lighting,BTA's don't really need intesnse lighting IME.My RBTA doesn't like direct 250MH lighting.Just let it be for a while,it will move about until it finds a place it likes.For feeding,I prefer mysis over silversides for BTA's.When healthy,their tentacles are very sticky.I just squirt a little mysis at it with a turkey baster and it sucks them right in.