I have a pair of tiger pistols and a coral banded shrimp in my 55 and they don't ever see eachother. The coral banded is always up on the rockwork on a ledge or something, while the pistol shrimps and their orange spotted goby friend are beneath the surface digging away. They have tunnels that run the whole length of the tank. Just make sure to have a deeper sand bed of crushed coral so the pistol can bulldoze and tunnel to its heart's desire.