I'm sure someone will come up with a better idea but I'll still toss these out there lol. Mind you I haven't tried any of these so no idea if it'll work, but 1 remove said shrimp to another tank while growing out (will work but a pain) 2 section off the tank and grow out the HC on one said then swap the shrimp and do it on the other side. 3 get something like a loufa or however you spell it, and use the mesh to hold it down. Just like moss the mesh *should* be large so it wouldn't be too difficult to pull off once it's rooted and hopefully small enough so it doesn't float up every time your shrimp pick at it?
Just a few quick ideas, as I said I'm sure someone will come with the perfect solution shortly.
