In this compact lumpy form, all an Excel or H2O2 spot treatment reaches and destroys is the outer layer. Repeated treatments will slowly shrink it. On driftwood, even if you're persistent enough to get all the visible spots this way, it will typically reappear in short order. I believe it burrows into the wood, so no surface treatment can fully remove it.I tried the excel route but it didn't do a thing :I It's only on the driftwood though, maybe it's the source of the problem, like rotting?
Did you take any precautions about cleaning the PVC after using the sponge? I don't know if this is the best idea using cleaning products with aquarium equipment...Yes, it developed on beige painted PVC. I didn't scrub it off until it grew into little bushes. After dosing with Excel the remainder came off pretty well with a Mr. Clean sponge.