It does like like diatoms however my dinos also started off like that. Get a cheap 25/100/1000x microscope from amazon and have a look.
What's really jumping out at me is phosphate and nitrate being zero. Aim for 2-5 nitrate and 0.03 phosphate. They can be too low and this is known to trigger dinos.
edit: pic of the early stages, ignore the bobbit worm
it eventually progressed to this: