My pool is almost 8 years old and my pump has apparently burned out. It is a A.O. Smith Century Centurion, 3/4 hp. My pool is 18,000 gal. What is the optimum hp for my pool? I have a heyward sand filter. I also have a polaris pool cleaner. I have no problem changing the pump, but want to make sure that it is going to last and have sufficient hp for the job. Any help offered is greatly appreciated.