I don’t think it’s bubble algae. If you look closely it looks like air bubbles. If I’m right, I have the same situation in my tank. It started on the back wall and then one spot of the sand. Now 2 months later it’s getting all over my rocks. I just brushed it all off with a toothbrush, but I did that 2 weeks ago too and it just came back. My tanks about 8 months old. Nitrate ~25ppm and phosphate always reading 0.03 or under with my Hanna ULR.
I’m following to see what others say. The positive is that it’s insanely easy to remove. Perhaps just new tank syndrome for us both?
That stuff covered my sandbed at one point and I kept turning it over until I realized it wasn’t going away. I used chemiclean and it got rid of it in a day. So I am guessing it was cyano but since it is green it is hard to tell.