they only need light. they are photosynthetic. just good water conditions and lots of light
I have always been under the impression that zoos really need to be fed. Supporting that mucous membrane that they produce takes more energy than a simple light can provide.
I feed everything in my tank my own blend of "mush". I simply blended up fish, shrimp, oyster, fish food, squid, vitamins, etc.. and froze it. I then break off small portions, thaw it out and dump it into the system. Occasionally I will also target feed certain organisms as well to make sure they are eating.