I appear to have a Dynamo 2HP pump with a Sand-dollar sand filter.
I do not have a timer yet.
After a couple of hours or so, the water flow is noticeably less coming out of the return. Also, from looking in the skimmer there is less 'suction'.
The skimmer basket is not full, nowhere near it. The basket inside the pump is clean.
Sometimes, the flow practically stops to where you can hardly feel any water at all coming out of the return.
The sound of the pump does not change so it doesn't appear to be slowing down.
I can turn the pump off and wait a few hours and turn it on and everything is normal again.... for a few more hours then slows again.
Backwashing does not make the pump run normally longer. I see no leaks, no bubbling or air rushing through line.