Well I cleaned the skippy today. Took all of the pad out and washed them. The pads were covered with a material that resembled mud. Water would have had a hard time circulating around the pads if they weren't cleaned. So cleaning them was a must. There were a few little snails in the bottom and I found a little bit of gritty material like sand. I examined the grit and determined it was ground up snail shells that must have been broken up as the water swirled in the bottom.