I no longer have faith in my original ID. There was never enough detail of the front end to be sure. sorry.
I'm 50/50 on whether it's amphidinium or prorocetrum.
the snotty blobs are not the most common amphidinium presentation. They are more typical of proros. Amphidinium are more dusty.
Amphidinium look lighter after darkness too, because they go down into the sand. Anyway. I think adding UV is worth a try. I'm still unsure on which one we're looking at.
How many watt UV would I need for a 40 breeder?