Taken from a previous thread, this is what I have done to keep them and it has worked great for me.

Ive only had one Morish Idol die on me out of about 15 I have gotten in, and it didnt ship very well, died in a day... Get your blender out and mix up some clams, mussles, squid, spirilina, nori, mysis, and any other stinky fish food you can find, blend it till its mushy with some chunks, get out some dry small pieces of base rock around the size of your fist, and smear the stinky crap all over 1 side of the base rock, now you dry it in the oven with the oven on really low, once dry, put various food rocks in freezer bags and throw them in the freezr. After your morish idol has been in the tank for a day, drop one of the food rocks in and they usually go to town in a short time. If they still dont seem to be eating enough, I usually pull them out of the tank and put them in a water tray, similar to a baking pan, and I put a plastic syringe down their throat and pump them full of yogurt, mysis, and appetite stimulant, once Ive done that, I have never had another problem with one... After all that has been done, they get used to normal feeding procedures.

In addition to this I have had good success with feeding hikari mega marine angel, and mega marine algae