Detritus worms or blackworms, hard to tell without a microscope. They're harmless, actually eat your mulm/detritus, and are relished by many larger fish. After all, the first is an oligochaete, same as an earthworm.
Those "roaches" sound and look a lot like ostracods, haha. When you say they move like a roach, do you mean that they're kinda jerky like a flea? Have you ever seen daphnia movement - is it like that, but on the ground?
Ostracods are also harmless and another great food. Anything that'll eat daphnids would probably love them.