This is a total victory, it looks like the Carolina algae began not only to grow, but also to reproduce on the acrylic shelf. It's them, isn't it? So far, it is scratched quite easily with my fingernails. I'm happy about that, because I think it's a good sign that I've achieved good water quality.
Recently i was cleaning glass when i spotted strange 3-5 mm thing on my acrylic shelf. Maybe it looks like egg laying of my new turbo or small old patella snails, or it is just a some sort of white carolina (but not sure it even exists) finaly started to breed, that, as i know, a good sign too...