[dukydaf]

Hi, @AngeltheGypsy Welcome to the forum !

The plant can certainly be saved. Is the stuff on the leaves growing back ? Is it easy to scrub off? Is it more firmly attached ? Is it part of the leaf color ?

If bleached for ~2min in 1:19 bleach:water by volume than nothing but the plant should survive.

 

[dukydaf]

Cyanobacteria in freshwater grows like a green-blue slime . If you just rub your finger over it, it will go detach. So from your description it should not be cyanobacteria.

It looks to me like either dense green spot algae, green round spots that are very hard to remove (in this case high P seems to reduce them) or green-yellow leaf zones from low nitrogen.