If your tank doesn't have any pests in it, you can't get pests from over-feeding. That said, over-feeding a tank *may* increase the chances of said pests over-producing once they are already there! But again, there could be an infestation without any over-feeding at all... or any feeding for that matter. It really varies from tank to tank.
Cutting down on feeding *might* help. More water changes while trying to suck up the extra critters and 'gravel vacuuming' the tank may help. Adding fish that would eat them may help. (but fish might eat shrimp/baby shrimp)