Should the filter ever be run with the skimmer intake blocked (i.e. by a tennis ball)? The reason I ask is I have a problem keeping the water level above the skimmer. And with the California drought situation, we're trying to do our part to reduce excessive water use. I can not find the valve that shuts the skimmer off. If I do this, I know there will be more surface debris, but the water would filter more effectively. Otherwise, eventhough the pump is on automatically, it's just not doing an efficient enough job circulating water.