I'd try a water change first. What's the temp? I think slightly higher temps increase activity and breeding, so that might be something to try as well.
What's your filter like? If you're using a power filter with nylons or sponge on the intake, perhaps there is a rip and they're getting sucked in. Curious. I had something similar happen with my pond snails, but the cherries that were in the tank were fine. Turned out it was planaria eating the snail eggs, but they don't eat shrimp or shrimplets at all. I'm betting that a water change would help immensely. There's more to remove than just nitrates, and there might be other substances that are building up without showing any other signs.
What's your filter like? If you're using a power filter with nylons or sponge on the intake, perhaps there is a rip and they're getting sucked in. Curious. I had something similar happen with my pond snails, but the cherries that were in the tank were fine. Turned out it was planaria eating the snail eggs, but they don't eat shrimp or shrimplets at all. I'm betting that a water change would help immensely. There's more to remove than just nitrates, and there might be other substances that are building up without showing any other signs.