Dinoflagellates... Son of a...
Ok, so I've gotten the upper hand on these guys! It's not over, but I've definitely hit on some things I think helped:
Flow: adding the mp10 to the display was by far the best thing I think I did. My koralias on a wavemaker were just not cutting it. However, I believe whole-heatedly now that flow is the key. I put the koralias in my sump after putting the mp in my DT. They are all aimed up to agitate the surface:
I've noticed my pH isn't dropping as much and nothing can settle anywhere except my filter sock.
Keeping it from building up anywhere. I used a turkey baster to blast it off of anything it settled on.
Hydrogen peroxide. It did seem to help. I think mine took longer to help because I found out my bottle was about 6 years old. I could not find an expiration date or anything on it, but I suspect had I bought a new bottle, the effects would have been much faster.