Sometimes algae just gets out of control. No matter how many water changes we make, additives we dose, or algae we manually remove, it just keeps coming back. You’ve tried adding water flow. You’ve increased your magnesium to suggested levels. Sometimes, all of that stuff just doesn’t solve the problem. One solution that seems to work pretty well, at least for stuff like cyanobacteria and dinoflagellates, is a lights out period for a couple of days. All you have to do it kill the lights and make sure that ambient light doesn’t get into the aquarium, then after a couple of days turn the lights back on and do a water change. The fish and corals should be fine over the two or three day lights out period, and typically the algae dies back enough to manage. Also note that this method shouldn’t be a long term solution to an algae problem. It is merely a quick way to get it under control to some extent. If algae persists, it’s time to alter some things in the tank.