Are you certain that it is algal and not fungal/bacterial? It reminds me of the funk that grows on my airstone at the end of my CO2 line. Mine is snow-white at first but turns tan/brown with age.
But it doesn't seem to hurt anything or spread.
PS- Quite off-topic, but congrats on first post after 17 months being registered!
PS- Quite off-topic, but congrats on first post after 17 months being registered!