What are these things?
Hello, I believe that is a scud. They can be found in healthy ecosystems, but anytime Iíve seen them in an aquarium they are very hard to get rid of. They will eat everything that your shrimp would eat eventually out competing. They also go a step further and will eat the living plant leaves and mosses. The best way to keep the population under control is with fish that eat them. Manual removal is hard especially if you have shrimp in the tank as-well, and have to be extremely consistent daily multiple times a day when removing them.
I donít wanna say the only way to get rid of them is to do a complete breakdown and dry out of all ornaments, but the couple times Iíve had them this was my only way to get rid of them for good. They can come from plant/fish/snail orders, ornaments or equipment that came from other tanks and didnít dry, and collecting anything from outside streams/ponds.