Do scallops sting corals

Correct. However the fact that it's moving around to much can mean that it's being bothered by something which the scallop may think could be a predator.
Usually when they are comfortable they would somehow attach their foot to a rock and just sit there till it wants to move again. Kind of like an anemone.
Supodedly survival rate is pretty low when captive for the same reasons you mentioned of having a "dirty" water habitat. I've had mine for about 2 months now, and hoping it will last me lot more lol.
They like medium to high flow. It makes it easier to eat. If I remember correctly from the disection we did in my class they an incurrent siphon by wich the food that flows through it gets stuck in their gills and then passed through their mouth then it's processed and then excreted through their excurrent siphone.
Something like that.

 

I don't know about that, I read it reading up on what I was getting into with this impulse buy. LOL