Well without knowing which one it is I’d have to say start with these things;
-Run Carbon
-Definitely run UV if you’ve got one, if not it’s a good idea to get one if you can swing it. It’ll help with a lot more than Dino’s
-Make sure there is no direct sunlight lighting the tank or even a lot of ambient sunlight
-Dont do water changes, they feed off certain trace elements in the salt
-Manual removal and keep your filter socks/pads changed out daily
-0.0ppm nitrates and phosphate are a bad thing, they thrive off an ultra low nutrient environment. Shoot for at least 1 ppm nitrates but 5 is better. (But be careful not to get there too fast, you don’t want to overwhelm your tank and then end up with an algae break out
-Run a refugium
-And if you can get your hands on some acartia copepods they will help eat them.
This is just what I’ve done to beat it the times I’ve ran into it and it’s worked every time I’ve dealt with Dino’s (which has been a good handful of times over the last 15 years). But, there are other types out there that I haven’t dealt with so I can’t say this will necessarily work for you without a positive ID on which type you’re dealing with. Your best bet is to get your hands on a microscope and get some good pics or better yet a good video.
Hope this helps, let me know if you have any questions. Hopefully one of the Dino experts can chime in and give you better advice.