Antique Filter?

[DewKiss]

My mother purchased an above ground pool from a neighbor, and had it moved and set up by a local pool company. She has never had a pool, and my brother and I know very little about them. SO....the filter and pump seem to work fine, as long as no one gets into the pool. As soon as someone gets in, or there is any water movement, the flow from the filter drops dramaticaly, as well as the pressure. The filter is this tall thing with a priming handle on top, but the inside has a bunch of long "fingers" that hang downward inside. (It's also a sand filter) Does the pressure drop indicate that it is sucking air somewhere....or is this filter just incredibly old and needs to be replaced?

[Pool Filter]

The pump is either not able to suck up enough water or the return line is being obstructed. Or the pump may just be dying .