sorry kind of vague
. normally they filter water, but if there isnt enough in the water they'll forage around for food on the ground. i have some wardleys shrimp pellets, and works pretty well. it breaks down to the point of almost being fully suspended in the water if you put enough in, and leave it there long enough.
how long have you had it? if its lying on its side, im sure its something more than food.