A long time ago I had a pair of Yellow Watchman Gobies. I made them a burrow by Heating PVC Pipe and Squeezing it into an oval. Later on I added a Pistol Shrimp. Only one of the Gobies paired with the Shrimp, which caused squabbling. I liked to have a Paired set with a Shrimp. Need some advice. Also Currently in the 120 Gallon, 4 x 2 x 2, are a Yellow Tang, Vox Angel, Flameback Angel, and a Neon Cleaner Goby.