Don't quote me 100% on this, but I think in the first couple days, the skimmer can remove it from the water column as is normal. I think after that, much of it will be absorbed by the GHA, which is why you're able to use the skimmer again. Even though it has been absorbed by the GHA, it is pretty slow acting. I had bryopsis in a nano and Fluc cleared it up within about a week. I'm currently treating some unidentified GHA in my other tank and it's slowly but surely working. Pushing through my second week now.
I kept the skimmer off for 4 days, but ran GFO and biopellets which don't affect the treatment. The GHA hasn't gone white and died off directly, but it has stopped growing, is easy to pull off the rocks, and is getting smothered out by cyano. I'm basically letting the cyano choke it out, then pulling it off in sheets, showing clean rock underneath.
My cyano isnt running amok, only growing on the dying GHA, so it's a pretty convenient helper right now. Keep up with manual removal and if you must do a water change(to siphon dead algae or whatever) then dose more fluconazole based on the amount of water you replaced. Between my 2 large rocks that were both covered, 1 is now algae free and the 2nd just has some wispy stuff left on it
