All that white is exposed skeleton that wasn't exposed before. Everywhere you see the hard white is missing flesh from damage. Toothbrushes do not belong on LPS corals.
You're right about the best and worst case scenarios. Make sure to keep your water as clean as possible, without draining the nutrients too much. If there's intact heads on the other side, feed those only, not the damaged heads.
Oh, and for zoas, a peroxide dip can remove algae without needing any scrubbing. You have to be careful with those, because some species of them are toxic, and scrubbing with a toothbrush will spray teeny-tiny particles of slime everywhere. Bad if the slime is toxic.
Hey, at least you've got a good "when I started out in the hobby, I ____" story! And it doesn't involve the suffering and/or death of an animal with a brain. You've basically severely inconvenienced a plant.