I have an AG 18ft by 4 ft pool. I currently have a 100 pound Columbia sand filter that I wish to upgrade and I have a 3/4 hp pump which I understand is an ok size for my pool. My question is which sand filter should I purchase, I do wish to continue to use a sand filter. I have heard that Hayward is the brand to choose but what size? I assume I should stick with a 100 pound sand filter. Thanks for any suggestions.