Mmm, a couple days ago I looked into my fish tank and my betta was gone. He was gone for about 3 days, and when I put food in on the 3rd day, the gravel in the far left corner of the tank started rumbleing, and my betta swam up to the top , ate, swam down to the corner, and buried himself again. What's he doing? Has anybody else had this sort of problem?