We had a cartridge on ours when we moved here.Finally got a sand filter.The cartridge according to the pool people we use is for pretty much hot tubs and spas not pols.they ysed to use them pretty much because they were easy to get.Our hayward sand has been omn at least 6 or 7 years and all we did was add some sand./Just use the pool sand and not play sand.The cartridge we had were pricey Buy maybe one or two and you have a sand filter.yeah we washed them but they never filtered as good as sand.Rocky