I give flakes in my tank for my fish and the sharks don't eat them as they are always at the bottom of the tank. So, I got pellets that sink. I drop the pellets right next to the sharks and they'll only eat 1 or two of the pellets, sometimes none at all. The pellets just sink and decay on the gravel. I feel like the sharks aren't seeing the pellets. What should I do? Also, the sharks are about 6 inches long each if that helps