If your Pump is 12Vdc, reduce the 120 to the 12V supply?
If you have a 12V supply for the pump, it's only 65W= (65W÷12V)=5.4Adc on the output side of the supply.
If the supply is around 80% efficient, the power in is 65W÷0.80=82W.
Line voltage of 115Vac, would be required to furnish 82W÷115V=0.7Amps.
A lamp dimmer could handle the power of your existing supply, and if the existing supply is a common wall wart, it has a transformer which can handle a standard triac lamp dimmer. So try a lamp dimmer to reduce ac voltage going to your 12V supply?