I am dosing Silicate as suggested. Phosphates are currently elevated so I am backing off on this for a bit. UV is running and I am dosing Microbacter7 each morning. We had Mike Paletta at our FMAS group meeting last night and he suggested Hydrogen Peroxide on the hot spots on the sand bed. Using a turkey baster. What are your thoughts on this and do you think it will even make a difference or just keep pushing forward as I currently am. On a positive note I did notice some improvement last night, I think. There seemed to be less coverage on the sand.Looking at your videos in the last post, we can see why the UV has "done nothing". What you are now posting is Large Cell Amphidinium, the kind that does not go into the water no matter how much encouragement you give it. They go into the sand instead.
In reality your UV/blackout did do something - it knocked out your earlier species, and left only the population that is not susceptible. I would continue running UV since you almost certainly still have cells of other kinds in your tank, but your main issue is now large cell amphidinium.
MB7 is not a terrible idea. Some have had success with it, and it doesn't seem harmful. This kind is not typically toxic. Hopefully The UV knocking out the water-going types will keep the dinos off the surviving corals.
Here's a thread on Amphidinium specifically.