looks like that particular rock is leaching PO4. if nothing else is on that rock, i'd dip it in H2O2 for 1 min, and scrub it clean. the bacteria will recolonize in no time (if your LR has properly cycled) or you could also run GFO and GAC (if you're not already.)
Added Hermits. emerald green crab and turbo snails. They have been in the tank for 3 days. Not much progression yet. Algae seems to be spreading. I hope they will get it under control.