Hmm, I tried magic eraser on GSA years ago without good results or maybe it was green dot alga, is it different? Is there a special technique? Maybe I just expected "magic", lol.
Well, I'm not sure that it really matters, but the "not for aquarium use" is on nearly every packaged scrubby I can find. I located these online, and ordered some. They do seem really nice and I think I will stick to them just in case. They are made for the aquarium: