I think I cracked the case, which possibly could be why plate corals in general don't do great while glued down to frag plugs. The answer is algae- that diaseris plate had a tuft of GHA right next to the coral. I realized this because I had an issue with my orange diaseris that i was keeping- it was doing great for a while, then suddenly one day it's all deflated and sad. This time, however, I noticed the hair algae that was brushed up against the plate, so I took a toothbrush to the area around the plate on the frag plug and got off everything I could, and the next day, as if it was magic, it was open and happy as ever.
Something about plate corals in particular I think makes them extremely sensitive to algae growth around them- they usually have no exposed skeleton, so there wouldn't be any place for algae to grow even if it wanted to. However, once there is skeleton exposed (or a frag plug- pretty much any surface where algae can grow), the coral fades away as algae blooms on it. People usually say that when a plate coral on a frag plug randomly does poorly, it's because they suddenly want to move. I conject that it has to do with algae growth, not the sudden desire for a coral to move around, since both of my corals were happy as could be in the place they were before they started fading away.
started target feeding aminos
