I have a 33 gallon FOWLR setup that has been up and running for approx. 8 months now I think. First SW tank I've done, but I have some previous experience with FW. Live sand, about 25 lbs of live rock. Currently it is home to a flame angel, a bicolor blenny, a lawnmower blenny, 3 green chromis, a firefish, a cleaner shrimp, a tiger pistol shrimp, assorted nassarius snails and an astrea snail.
Now the problem... you may have noticed I didn't list a shrimp goby for the pistol shrimp. I did get a black-ray goby with the shrimp, they were happily paired and I would nearly always see the goby at feeding time and sometimes out keeping a watchful eye as the shrimp was digging their burrow. This lasted for a few months and everything seemed fine.
One day I realized I never saw the goby anymore, and more suspicious I would see the pistol shrimp poking his head out by himself at feeding time - no goby to be seen. This went on long enough (several weeks) that I assumed something untoward had happened to the goby, so I purchased another one (same kind) and introduced it to the tank.
After adding the new black-ray goby to the tank, it sat at the bottom for a bit before disappearing, into the rock and the shrimp's tunnels I assumed. However, I never saw it again after that, and I continued to see the shrimp by himself. This was about 3 weeks ago now that I added the second goby, and I have to assume it is no more as well based on the behavior of the previous one (you think I would've seen it at least once since adding it to the tank!).
What could be happening here? I've noticed there is a fairly large (at least 5+ inches of it that I've seen) bristle worm that I've seen at night halfway out of the shrimp's burrow entrances from time to time. Could that have something to do with the disappearing gobies? Is the shrimp itself harming them? I figured both scenarios unlikely, but I'm unsure what to think anymore.
I'm reluctant to buy any more gobies if they're going to just keep disappearing, but I sort of need one for the pistol shrimp. Does anyone have any idea what could be going on here? Water parameters etc all seem fine. No other fish have died.
Thanks for reading and replying. I'm at a loss here