I have a gunite pool with fiberglass sides...Between 25,000 and 30,000 gallons...Currently have a 0.5 horsepower pump with a 36 square foot Sta-Rite DE filter. I have been told to look at sand filters that hold about 300 pounds of sand. I was mostly questioning the place that told me the pump would need to be replaced as well, which didn't make sense to me at all.