Whatever they are , they don't look pretty and can take over your tank very fast
Google "dinoflagellates in reef tank" - this is one of the images from that search
That's what I had. Luckily the blackout worked. I think It helped that I got to it early. I had a large die off in my tank that I think sparked it. I can't be sure but when I was doing my research others reported that they had things die just before the outbreak. I hope they never come back!