Do you have a microscope to diagnose for sure that it's dinoflagellates and not diatoms? You can also sometimes determine what species with a microscope and different treatments work better on different species. I had mostly ostreopsis and what finally worked for me was a UV sterilizer and 3 day blackout. They actually just came back in the past couple days after two to three weeks of inconsistent care because I was out of town a lot. I think the main thing that made them bloom this time was a lack of nutrients as I wasn't feeding for days at a time in addition to scrubbing off a bunch of nuisance algae that might have been using nutrients before the dinos could. Basically, things got just slightly off balance and they came back. When I got rid of them the first time I also added different types of bacteria, pods, phytoplankton, and macro algae after the blackout to try to diversify my micro flora and fauna.
