Mr. Clean Magic Eraser. Make wet, wipe (do not scrub), wipe again with a dry cloth. Comes right off. If needed, wipe the Mr. Clean a second time. Resist temptation to scrub. Works wonderful. So small areas at a time, start in one corner and work you way across. You'll not have mold for a long-long time again. Been using Mr. Clean Magic Eraser for over 10 years now. Use it twice a season. That's all.