Paul decided the plants and rocks filtering the fish tank needed to be cleaned.  After tackling the chore he decided cleaning the  sludge off the rocks that the plants rested upon was awfully tedious.  As he so often does, Paul decided there must be an easier way and set about figuring out just what that way was.  As it turned out he removed the rocks from the garbage can lid, leaving just the plants to filter the fine sediment from the water and the strainer to capture the larger pieces of sediment. The plants, once again, demonstrated their ability to clean the water as the tank is again clear.