You know I have the same algae in my tank. It's just growing on the glass. I have quite a few snail in my nano and they can't get it off the glass. I've had to resort to utilizing a plastic putty knife to scrape it off the glass and suck it out when I do a water change. It just keeps coming back in force. The only difference that I've had with my tank is I moved it from one side of the room to the other. I initially thought it was because there was some sun hitting it but I remedied that quickly. I've watched the snails as they are eating off the glass and they aren't even coming close to making a difference on it. They for some reason can't bite deep enough to get it off. I'm not sure what to do and I've tried the changing my light timing. Didn't make a difference. And with my anemone and clam in the tank I cant just turn the lighting off for a day or so.