Hmm... From what I've read, they don't tend to become bloated very easily. I currently have 4 in my 55g along w/ a mated pair of WC chaitika yellow comps. I have noticed That they dig quite constantly and, like yours, about 3-1/2 ft. across the front of my tank they have mounded the sand almost 6 in. high. I have been debating on whether I should smooth it out or not, as this may be a part of spawning.? Not quite sure why yours hid all the time, but mine are out all the time, and only retreat when my 3 yr. old approaches the tank (I laugh at this quite frequently, as none of my fish really seem to enjoy his presence)