Strange gnat-like creatures

[IslandCrow]

A swarm of gnats in my aquarium is the only way I can think to describe these things. I only see them a few hours after the lights have gone out. They're very, very small. Each one is less than a millimeter across. I managed to get a few of them out of the aquarium, and they have clear bodies with a black spot at one end. Without having a microscope, I couldn't see much beyond that. They stay pretty close to the sand, but seem to be able to swim. As small as they are, it was very difficult to get decent pictures or video, but here's what I was able to get. In the video, they're the small black things swimming around the astrea snail, which is about 1/2 inch across for reference:

Video

 

[IslandCrow]

Here's one more I took with my 2:1 macro. It didn't turn out very well, but I doctored it up a bit in Photoshop. The contrast is a bit exaggerated, but it gives a little more detail:

 

[mystikdragon7]

Hard to tell from the pic, but they look like mysis shrimp.

 

[IslandCrow]

Yeah, I figured they'd be a pretty tough ID. Hopefully they're just something like mysis. They don't look like any of the pest creatures I've seen.

 

[Riptide10]

That last picture is excellent. It's to early to say for certain what those are IMO.