LOL, there's a reason why the customer "traded them in." They're crazy fish!!! They're going to sift thru your sand bed and stir up sand onto your live rock. Defintely a fish that is to be avoid if you have corals. If you have only a FOWLR tank, then their okay.... but they can still cloud the water when they sift thru the sand. That's why they're called "engineer" gobies. I had one, and after a couple of weeks, had to break down my tank, remove all my LR and corals, just to catch the terror and offered it for free locally. Even for free, reefers avoided the fish! LOL.