I just came from there, having bryopsis for the second time. This time, it didn't exhibit the feathery appearance until it started to die. I've also had it before, I knew what it looked like, and I was fooled. Hair algae would be weakened by three days with no light. Bryopsis won't skip a beat. I recently had three WEEKS lights out on my FOWLR, and it didn't die. This stuff is tough, and sneaky. I dose vodka, no nitrates, no phosphates, urchins wouldn't eat it. Algaefix killed all algae, even the chaeto, but not the bryopsis. I STILL thought it was gha at this point. With the absence of other algaes, the "gha" started to take off. Eliminate all other factors, and the one which remains must be the truth. Doubting that it was bryopsis, I raised the magnesium to 1,800 with Kent Tech M, and the bryopsis slowly started to die. It took three weeks for it to start to fade. Any other form of magnesium has not worked for me. With all due respect, someone here makes a pretty good case that it's not GHA: none of my fish will graze on it I've never had any traces of phosphate or nitrate I got GHA while vodka dosing was going on too.. I've gone thru 3 sea hares...none of which ate my algae.... my tangs don't touch it...Yellow tang, Hippo Tang, Chevron Tang, Unicorn Tang...none of them...also on my 3rd foxface... I have tried a black out...for 3 days...with nothing.