I have an Easy Pro 250 pump in a Savio skimmer filter box. Occasionally the water in the pump chamber will drop down to nothing. Meanwhile the water in the filter basket section in front of the pump is right up to pond level. I can figure out why the water in the pump chamber of the Skimmer filter does this while the water stays high in the basket. Does anybody know what the problem might be and how to fix it? The red arrow is pointing to the pump chamber. TIA