Not shrimp?

I feel fairly confident that the smaller organisms swimming around my plant tank are not baby shrimp. I'm guessing they're some sort of cladoceran that got introduced either with the plants or the fish or shrimp or, for that matter, on a rock, in some dust... The unusual thing probably isn't getting things like that into your tank, it's a matter of their finding predator-free space. The current inhabitants of the tank (Cherry red shrimp, pygmy corys, Otocinclus) aren't going to both organisms that stay out of their way. Adding a prefilter also makes the tank more friendly to smaller organisms.