I got a horrible outbreak of cyano/BGA in my 90 gallon a few months back... so bad, I almost got rid of the tank! We went the non-chemical route. One thing I didn't see mentioned is reducing your feedings (either frequency or amount or both). We had been using a couple of Brightwell Aquatics foods for corals and filter feeders + Kent ZooPlex, as well soaking our food in Guarlic guard and another Brightwell Aquatic amino-somethingarother. We stopped using all of the above. We also started straining all our frozen food.
Our vacuum wasn't strong enough to suck the stuff off the rocks - but I foung Q-tips worked extremely well. I won't tell you how many boxes of Q-tips we went through!!! We had two Koralia #3 fans but only had one turned on (I was convinced it would blow all our poor little fish all over the place). Anyway, we turned on the second fan and the fish did adjust (silly me).
Anyway, reducing our feedings, not using liquid foods, increasing circulation and getting more out of our skimmer worked well for us.
Good Luck!
Jennie