The advice provided regarding pump size for your ~3400 gallon pool is very good. I would also like to suggest that a 40 sq ft cartridge filter is somewhat small -- not unusual when purchasing standard equipment for a small above-ground pool. If you have opportunity and desire to upgrade your cartridge filter, look for one that is in the neighborhood of 100 sq ft; that's a better match for your gallons/area and you'll find that you don't have to clean it as often. Of course, just replacing the filter media (cartridge) may help with your problem.