I have a 18' round above ground pool 52" wall. Currently it has a sand filter. My friend has offered me a cartridge filter with pump. Should I take it? I'm not attached to the sand filter and we constantly have pollen issues in the pool. I have read that cartridge filter can save money on electricity. In the summer months (we live in northeast) our bill goes up $300 between pool and window a/c units. The cartridge filter is Hayward c550 and 2 years old. He stored it inside during winter and replaced cartridge every year. Do I replace them every year or just as needed? Also I use a salt generator, can I use it with this filter?