Try and fluff it off as best you can, doing water changes to get rid of it and addinf a bit more CO2 will help.

F F- got it right.

You can try a 2 day blackout + Excel + Water changes each day(no CO2 during this time).

Add more filtration perhaps also, prune some biomass back, clean well aftrer you do any large changes in the tank(water changes, filters etc)

Regards,
Tom Barr