No. The bright cells and dark background makes a lot of features unfamiliar. Can't ID from those.
That is crazy, and does not fit.
Ostreopsis
Thanks the ID! Is it normal for ostreopsis to be on the rocks and glass only? Nothing on the sand. And it does not go away at night, at least not that I notice.
This tells me the UV is not doing its job... at all. Those cheap ones can work, or easily be defective. I've used that model before. (You have the UV in the display, right?)
Some tanks under some situations, you can pour test tubes of live dinos into it (I've done it) and not have them take over. To me that's a sign of health - or at least resilience as far as nuisance outbreaks are concerned.
All of our problem dinos except for large cell amphidenium go into the water at night to some extent. How much depends on the nutrient strategies and habits of the particular type. Ostreopsis is the most prone to go into the water. Those kinds less likely to go into the water can be encouraged to do so by making their current habitat less comfortable, such as cutting the light and blasting surfaces with turkey baster. Ostreopsis also seek out higher flow surfaces to attach to than most other kinds. So it is much more likely to show up on rocks and glass than sand.
In the mean time, you can hang some filter floss in front of a power head in plenty of light and flow. You will be amazed what a large percent of ostreopsis will attach to the rough surface in high flow and good light. You can export huge numbers that way. I've called it "poor man's UV", but really it might be even more effective, because when you pull it out in early afternoon and wash it under tap water you export the cells whereas UV only kills cells and leaves them in the tank.
