So I have a couple red cherry shrimps in a fluval spec V 5 gallon tank and for some reason, the shrimp like to go into a gap at the edge of the gravel that sucks up tank water to cycle. They don't go into the filter because there is a sponge closing off the opening, but they take turns getting half way sucked in and using their little feet to pick around on the sponge and then flick their tails to get out and swim away. They voluntarily go in there and scavenge. I'm afraid that they will get their antennas brokern by doing this or that they will get stuck and won't be able to get out...any advice? Should I place a piece of sponge over he opening? Or is it fine to let them do their thing?