Black swimming dots during water change

[etspam]

Hi all-

This is just to satisfy my curiosity. Changed the water in some small freshwater tanks, and I noticed tiny little black dots that are swimming around. I'm assuming they're some sort of creature/insect or such, but have no clue what they are. I was wondering if they were shrimplets (RCS), but they should be at least 2mm in size, and these were <1mm. I normally don't notice when changing the water in my bigger tank, because the water is very dirty/murky from detritus and such. Any ideas? We don't have a microscope.

ET

 

[dudley]

Probably freshwater amphipods also known as gammarus or scuds. Not harmful, some fish will eat them. You may need to increase substrate vacuuming to control them.

 

[NoodleCats]

Could also be seed shrimp. They'll be small, round, and move smoothly through the water (as opposed to jerking around like cyclops would)

Theyre harmless though