Lighting and algae?

[asylumdown]

Nutrients don't help, but other than that I'm not really sure. Nutrients might explain why some tanks get hit like a bus and others just sort of limp along with it, but I'm not sure if nutrients are always the explanation for their absolute presence or absence.

I don't know much about dinoflagellate biology, they're a pretty diverse group of organisms so I suspect that some strains are accidentally pretty well adapted to living in aquariums the same way that aiptasia accidentally have the perfect suite of adaptations to make them a perfect aquarium pest. Some of the reason might simply be that you were unlucky enough to have introduced these guys on a coral frag at some point whereas this particular species wasn't in your tank before. But that's only a guess.