That look like dinoflagellates, I'm fighting them since more than 1 month.
I'm trying to starve them with vodka dosing. A good temporary solution I found is to blast them with a turkey baster. They are easy to remove. I would say give a good shot of turkey baster everywhere (except on sensitive coral), them do immediately a water change.
I heard when the nutrient source is gone to do a blackout, or to dose 1ml of hydrogen peroxyde per gallon per days, but I won't do this until I'm sure it's reef safe.
I heard too raising PH to 8.5, 8.6 with kalk
can help, but I think it's dangerous to play like that with the parameters...