I’m pretty sure this is Dino’s, potentially prorocentrum? They mostly seem to disappear at night but grow everywhere during photoperiod. Mostly on the sand and hair algae I have in the tank. Dosing nitrate and phosphate, no water changes, adding waste away once a week. Running a GKM uv light 24w (50 gallon tank). Turkey baster off rocks/algae twice a day. Lights mostly just on blues. Dosing sodium silicate every so often. Doesn’t seem to be having any effect so far going on over a month of treatment.