Snappy parameters

[Delphinus]

Kind of sounds like it could be cyanobacteria but it could also be dinoflagellates. Diatoms are more of a light brown dusting and I don't think you usually see a lot of bubbles associated (but you do with cyano and dinos).

You do not want dinos as it's an absolute nightmare to deal with. Very persistent, resilient to any form of treatment, and usually toxic to invertebrates (if your snails start dropping dead you might have dinos). And just incredibly gross to look at. They grow incredibly fast as well - you can vacuum the stuff out and within hours it will look as if you've done nothing.

Cyano on the other hand is usually a nutrient loading issue. Test your NO3, usually you'll find NO3 to be the cause of cyano (although there are other causes, but this is, IMO/IME, one of the more common causes).