I put this little guy in my 29 gallon tank at work two days ago. I hadn't seen him, but I saw some poofs of sand coming from under my rock, so he seemed fine. Today I came in and he was upside down on the bottom. A customer said they saw the fish eat something on the bottom and looked like he was dying. Minutes later it was indeed dead. Is this a normal thing that happens? I have live sand substrate and it does have some small shells in it. Is that incompatible with gobies? Pictures linked below.