I had that happen to me the heads that turned darker color stopped opening up shrank way down my emerald crab ate the heads that were dying off. It took about 2 full weeks for the frag to fully open up now it’s huge growing like a weed it has grown 4 times the size as when I bought it 2 months ago it was about the size of yours I found if your waters
good the less you do to your corals the better they just have to acclimate to your water and mostly your lights some corals take few weeks