I'm still going with this:
It appears as if you have little if no water flow from what I can see, just some filters on the tank. This alone will create a multitude of dead spots. Then if you look around the tank, you can see the algae forming all over the substrate and the walls to an extent. If you look at the brain corals, you can actually see the algae growing on the brain corals. A powerhead may save the corals.
They are stationary corals, similar to SPS, and most don't have the ability to just "get rid" of algae if it begins to take over their fleshy parts. They will instead just shed their flesh. Other corals with certain tentacles, have the ability to somewhat "shock" the algae spores and get rid of them - obviously these don't. A prime example is the pink one that has the green spots all over it.
Getting rid of the what is causing the algae to thrive is a number two priority cause it can take a little bit. Getting the algae off of and away from the corals is probably the #1 priority if you want to keep them.
