Sounds like Cyanobacteria
Not worth your hassle to buy CUC for Cyano. They won't wipe it out, only nibble a little and not your solution.
You have some issues with your water nutrients and probably not cycled.
You can siphon some of it off, use Red Slime Remover product, but ultimately ... Improve your water, do water changes and wait it out. It is the ugliest!