Interesting product--that's a new one on me. After reading up on it, I would guess it won't harm your marimos. It seems to be an extremely efficient oxygenator which kills algae spores in the water column, keeping algae from spreading. I don't think it would have any effect on a marimo or other established plants (including established algae). It would simply keep the algae from reproducing, assuming that it actually works. A UV sterilizer does essentially the same thing, and is probably more effective.