Ya that is what likely happened. I thought with a tank if you plan to have fish that burrow in the sand you need to have "sugar" grain type sand. Basically no sharp edges like a crushed coral or larger rock style substrates. Im no expert thats for sure but I would guess that is what happened.. I dont have any experience with burrowing fish, im just getting to set up my 90 gal
and am planning to get a fish or two that burrow so I was planning on using the carib sea aragamax sugar sized sand. You might want to try and get out any of the larger/sharper pieces you can see. Hopefully someone with more experience with this will chime in soon too..