This week, I got a new dino outbreak in my new 250-gallon tank after dosing chemiclean for Cyano in the sand. Honestly, I’m not even scared of them anymore, and I'm happy about them replacing the ******* cyano. I’ve battled pretty much every common type of dino in my tanks: Prorocentrum, Amphidinium (small cell and large cell), and Ostreopsis.
Keep phosphates above 0.1 ppm, nitrates above 10 ppm, and dose silicates. And I mean A LOT of silicates, and they'll go away shortly.
In my previous 70-gallon tank, I think the recommended dose was something like 1 ml per week. I was dosing 10 ml daily for close to a month. Now, with the 250-gallon, I’m dosing around 30 mL daily. The only things I’ve noticed from dosing that much silicate are the dinos receding and a lot more sponges growing. Nothing else in the tank seems to be affected.