I had bought a rock full of yellow polyps (yes, yellow polyps not star polyps or star burst or sun polyps) that seemed to be doing nicely, until my LFS informed me that I should be feeding them. They suggested phytoplankton, which I bought and tried giving them. When I did the couple times I did, they immediately closed up and wouldn't open back up until the next day. Now they have been dying 1 by 1. I've stopped feeding them, but they still are dying off. Any thoughts on why they'd be dying off or how to stop it? My water params are fine with the exception of my nitrates which still sit at about 20 ppm, but they were that way before when the polyps were doing fine too. Any help would be appreciated.