A S325 cell is rated at 25,000 gallons and is really too small for your 19K pool. We recommend a cell be 2X your pool volume. The T-15 is rated at 40,000 gallons. You will need to run the S325 at close to 100% 24/7 to generate sufficient chlorine in the summer.
Welcome to TFP! For a wealth of pool care information please check out our free Pool School. If you are in need of specific help then we encourage you to Register and ask us here in the forum!