If the water is clear, add maybe 1/4 cup of DE to the skimmer with the pump running, watch the return while you pour it in. If there is a tear in your membrane or a bad seal in the filter, you'll see the DE come back into the pool. Also check that all the valves between the skimmer and pump are fully open, and that there's nothing obstructing the skimmer. Does it seem like there is more or less water flow than last year? If there is less, that would indicate a restriction between the skimmer and the filter inlet. If MORE water is flowing, that would probably indicate a filter issue.