I'd be hesitant to push MG over 1500, but that is just me. I think most of the evidence for high MG having a negative effect on bryopsis is pretty anecdotal. Where you are at now shouldn't be a problem with those alk and ca levels, as long as you are keeping them stable and they aren't swinging wildly. I would guess that your lights is the primary culprit, raising them is probably a good idea, reducing photoperiod is also a good idea. Lugol's reportedly can assist with light shock, it is dosed in very small amounts, be careful. I've used it before in similar situations but can't really say if it helped. Otherwise, I'd guess phosphate and nitrate levels. If you have a bryopsis issue, and 7 ppm nitrate, I'd worry about phosphates as well and maybe try and get them down a touch. 7 ppm in of itself isn't a huge issue, but if your levels are swinging around fairly quickly, it will definitely have an impact on your SPS. Only other thing I can think of is if your alk is being dosed right near your powerheads and is making contact with your corals before going into solution, that can be an issue as well. Hopefully you find the solution!
