Bob, that's interesting to learn; almost all of the filamentous algae in our pond floats in mats, uniformly green (thank heavens there are ever fewer of them); when I hit it with Cutrine it turns brown within a few minutes/hours, but doesn't always break up until I disturb it manually. What am I missing in terms of understanding its life cycle? (By the way--I think you ought to exercise adminstrative privilege and knock me down a couple of stars on the rating system--I'm sure learning what I don't know!!)