I have 20608 gallon inground pool - the pump and filter were cutoff at the pipes and taken; I need to purchase both and I’m total confused regarding the size: Since the pool volume is 20608 , the existing pvc plumbing is 1 1/2 inch pvc pipe. it has only one skimmer - the drain and 4 returns: I want to install a variable speed pump and a cartridge filter. For info: Length 32.3 ft, 18.1 Width average depth is 4.7. The skimmer plumbing is approximately 26.4 and the drain is 35.8. Thanks