Bro sorry to hear that!
I also met with quite similar problem. I stopped water change and change my gfo every week. Meanwhile manually removed free hanging gha and wash filter sock daily. The gha persisted for another 2 weeks but never grow or spread. But by 3rd week gha turned white and died off. No other chemical and reduction.in lighting was done. Of coz, I still lose a few sps. But up till today algae is at bay. Don't give up, as we know this is demoralizing.