Does anyone have thoughts on size of sand filter in relation to gallons? I just ordered a new filter, and replaced with same size I was using, although the specs say I need a larger one. I have a 1.5 hp pump and a 16 inch filter( 100 lbs sand) and my pool runs right around 20,000 gallons. It did fine for 10 years but recently sprung a huge leak. I appreciate anyone's thoughts on this.