I just purchased a Diamond Watchman Goby because I wanted to keep my tank as clean as possible. The first invert I purchases was a small horseshoe crab and I love him. He's certainly let my favorite creature in the tank. My question is, in a smaller tank (20G long) will these guys compete over food? The horseshoe crab often stays buried under the sand and doesn't clean it as I had hoped. I just don't want him to starve. What should I do? Trade the Goby and get hosed at the LFS?