Salinity is at 1.024 right now. I usually keep it at 1.023. The alk was only on the high side of normal. (It wasn't dangerously high by any means.)
My crabs are out in full force right now, I haven't seen so many so active at one time. And the rest of my coral are the happiest I've seen them yet, fully extended.
As for the hitchhikers, yes they're quite ugly but they've been with the coral for about 4 years, so if they're the problem then it's a recent development. They have plenty to eat, if anything I'm overfeeding.
Anyways, I think I've formed an idea of what may have happened. The exploding coral is in shadow and probably needed more light to survive, and died. It may have created an ammonia spike, therefore killing several snails, which I believe are quite fragile to spikes. Does this sound like a possibility?