Wire brush and scrubbing is really what you need. I have been battling this s**t for a coupe years. It started for me when I got new lights. Anyway...finally have the right combo of light and photoperiod and it is finally coming under control. The hydrogen peroxide s a good point...I would pour that on...soak it, once it starts to due of...scrub it den. But you gotta fix the original problem or it will come right back.