what lighting do you have that under mellow? mine does fine without co2 and is under the water line. i haven't had algae on it... but i have to shade my java moss otherwise it gets covered.I have it in a couple of tanks. it's really a slow grower and has proven itself to be quite susceptable to algae growth without co2. where it really flourishes is at or above the waterline, where it grows really nicely, a lot like a lichen.