market prawn is a very meaty food. thus have a very complex protein structure, making it very difficult for the coral to digest. if u feed it too often, the coral can actually die from over working itself just to digest the food...thats why reccomended feeding of once a week, or once every 10 days or so, and feed it small enough for the coral to eat. if u want to feed it more than once a week, then make sure u cut up the piece of prawn small small. dunf eed those big big huge piece and watch the coral struggling to eat. most of the time if its too big they will just spit it out.
the green coral u mean the big piece that is leaned against the wall? that is a favia coral. its an easy coral to keep. good lighting and moderate/strong flow. they extend their feeding tentacles at night, so if u wish to feed them, u have to do so at night, or u can train to get them to feed in the morning. u can feed them mysis. they have small mouths.