Magnatek is the MOTOR on the pump, not the pump.

It's very, very common to match an undersized sand filter with an oversized pump. When this happens, fine particles are blown THROUGH the filter, AND, sand tends to be blown OUT of the filter during each backwash cycle -- so the problem gets worse over time.

The immediate solution is to slow flow through the filter, by throttling a valve DOWNSTREAM of the pump.

The longer term solution is to (a) check and add more sand if needed,, and (b) replace the impeller with a smaller one. You can run a 1HP impeller with a 1.5HP motor with no problems, and only a slight loss of efficiency compared to a 1 HP impeller with a 1 HP motor.

But, to accurately size things, we'd have to known which PUMP you have, have a complete equipment list, and see some photos (you can mail them to poolforum@gmail.com) of your pump / filter / piping.