Thanks, folks!
SPC, yes the watchman gobies do get along. I got them as a "pair," since they were sitting together in the same cube at the pet store. I think I might have a mated pair because one of the fish seems to have a heavier more "macho" looking head to it.
tetra, the xenia does pulse quite well. I don't know if there's any secret involved, it just seems happy. I do keep the specific gravity on the high side (around 1.026) and I don't do water changes much. They probably like the high dissolved organic content for all I know. When I take some to one of the local pet stores for credit, they still pulse in the display tank but don't seem to grow much, but they use a BIG powerful skimmer.
The tank was set up in 1996. It sure has had its times of looking awful... had a huge bryopsis outbreak at one point.