I have a colony of dendros (they came with my 90g), and I love them. The guy I got them from, he'd got them off this guy who was starving them. Poor little dendros, their tissue is receded and one of the polyps, appears to have been quite large given the size of the skeleton at that part, died from starvation.
Anyways, I find my dendros really easy to care for. I'd set the little guy on a hard surface (live rock, frag rack, etc.) with low–moderate lighting, and moderate flow. I'd recommend feeding him a SMALL amount everyday. I'd recommend a mix of chopped silversides, frozen spirulina enriched brine shrimp, mysis shrimp (either whole Hikari or chopped up mysis from a better brand), chopped bivalve, clam eggs, etc.
Anyways, when you see him open, suck up some of the meaty blend with your target stick, then suck up some tank water so the portion's the same temperature as the tank (the polyps hate cold food being squirted at them), then gently release some of the food onto his polyp. Don't feed him too much or too large of pieces, as dendros can die from gut rot. As each day passes, he should start coming out more often and his polyp should become more robust, and after a couple of weeks, his tissue should start slowly regrowing. My guys' skeleton was devoid of tissue when I brought them home, but now their tissue is slowly starting to cover their skeleton again.
To encourage shy polyps to come out, I gently blow water onto them with my target feeder.
