Also iodine is important in their molting but I don't think I would supplement it just make sure you are up on waterchanges.
I had my skunk cleaner leap out of my 20g the other day, I was glad I was in the room as the dog was licking it.........I scooped him up and put him right back in the tank and he hasn't seemed to have suffered any ill effects from his flight of fancy....
Yes your shrimp should grow back his anntena within only a few weeks. This has happend to mine a few times when he got to close to my porcalin crab trying to steal his food... claw... snip snip... there goes his anntena!
lol...yes my 20g is topless.......no jumpers in there at least I didn't think so. I was standing there and heard a funny noise....it was my corgi licking the shrimp flopping around on the carpet. I just scooped him and put him back. He is one of my favourites so didn't want to lose him.
Shrimp like crabs and others in this family have the ability to regenerate limbs etc. If they lost a leg they would grow another, it may take a while but they will grow back.