Snappy parameters

[Delphinus]

That sounds more like cyano then. There are a lot of different colours cyano can be, red, brown, green, black (and, presumably, "cyan" given the name although I haven't seen that particular flavour).

A dinoflagellate bloom is rarely, if ever, contained to a few sporatic spots .. they can double in population in a matter of hours (if not minutes) so you can well imagine how fast a tank can be completely overwhelmed. Then they completely disappear at lights-off only to start again the next day at lights-on. Cyano, on the other hand, will also ebb and flow with the photoperiod but seems to be a lot slower.

Cyano feeds on nitrates (maybe to an extent PO4 as well). Do you grow out any chaetomorpha anywhere? Chaeto can be useful tool for sucking up some of that NO3/PO4.. (If you want some let me know I can get you a handful of it .. that's all you'd need. I grow mine in an aquaclear lit by 2x9w PC's and the stuff doubles in size about every two weeks.)