gray slimy algae

I take care of a 200 gallon reef aquarium. It has a refugium that is lit about 12 hours a day, protein skimmer, and 3 large bubble sponge filters. Water parameters: SG 1.022 it usually is 1.023 Temp 82 degrees PH 8.2 AM 0 ppm Nitrite 0 ppm Nitrate 0 ppm Calcium 480 CH 12 dkh Phosphate 0 ppm...