Fast moving algae, microscope pic - ID please?

[Reefer Dan]

Hello. My tank had Chrysophytes, but those have died off (4 month old tank). Now I am seeing some brown stuff in the sand and thought it was diatoms. This stuff is spreading fairly quickly on the sand. Any IDs? This is about 400x magnification.

I cannot get the video to attach and work, but they are fast/ high energy movers.

 

[vetteguy53081]

Hello. My tank had Chrysophytes, but those have died off (4 month old tank). Now I am seeing some brown stuff in the sand and thought it was diatoms. This stuff is spreading fairly quickly on the sand. Any IDs? This is about 400x magnification.

I cannot get the video to attach and work, but they are fast/ high energy movers.

Hard to tell under heavy blue lighting

 

[Just John]

Are they a brownish color or definitely green?
Are they there in the morning or go away at night and come back as they day goes on?
Any snotty stuff related to them, or just this stuff on the sand?

 

[Reefer Dan]

Are they a brownish color or definitely green?
Are they there in the morning or go away at night and come back as they day goes on?
Any snotty stuff related to them, or just this stuff on the sand?

No snotty stuff, just in the sand so far. Visually to the eye they are a brownish color. Under the microscope it was yellowish green.

 

[taricha]

Seems to fit this description...

These are not a dino. They are another random harmless flagellate. Something like a cryptomonas / rhodomonas.
Here they are in a couple of vids from my system, shape and movement a lot like yours:

(Close-up):