Algae ID / Do any diatoms enter the water column at night?

[proace360]

I've been dealing with brownish/yellowish algae on the sand bed of my tank for a couple of weeks now. I stupidly just blew it off before taking pictures so will add some later.

The algae doesn't clump together or form the strings I've seen other pictures of dinoflagellates and appears very powdery, but the thing that is throwing me off is that the algae disappears completely at night and re-forms in the morning like I've heard dinoflagellate do. I have a microscope and have tried to get samples of the powdery stuff, but I can't seem to have large enough concentration in my samples to find anything. I have a single video taken with low magnification showing a bunch of movement but after probably 10 tries it's the only video I've been able to take of anything. I should also mention that the organisms appear TINY compared to pictures of dinos I've seen. Also, my nitrates are pretty high (20 ppm+) but don't have a phosphate test yet (comes on Wednesday).

Anyways, I've been trying to ID this for awhile now and I'm stuck completely in the middle of whether they are diatoms or dinos. They behave like diatoms except when it comes to disappearing when the lights go out. Are there any diatoms that do that too?

I really wish I could get better microscope pictures/videos. Ugh.

 

[proace360]

The algae in question that disappears at night. It's typically more concentrated than this but probably looks not as bad since I blew it around not too long ago

 

[proace360]

Finally got a (very slightly) better video of a dino. It's hard to see in the video but I saw a beak-like protrusion on it so I'm 90% sure it's large cell amphidinium among a sea of diatoms. Not sure why it disappears at night though since they apparently don't go in the water column when the lights are out?