I have Pentair WhisperFlo filter with A.O. Smith 3HP Centery Pump part #7-177453-03. Seems the replacement part is #B2844. Do I need 3HP to run a  25000 gallon gunite pool with a caretaker in floor cleaning system? Or can i get away with smaller pump?

and while we're at it, if I wanted to upgrade to variable flo pump  motor, could I attach variable motor to existing whisper flo pump.