I have a 33' round above ground pool with a cartridge (new)filter . Its about 4 years old I cannot get the water(which tested perfect) to clear up. we had air bubbles in the lid of the pump i replaced the o ring which helped with the bubbles. it has good flow at the return but the filter is rarely dirty and the water has not been clear in over a month its as if the water is bypassing the filter. it used to be when i took the lid off to clean the filer there was always water in the tank but now its usually about 1/4 full is that normal? i have tried water clarifiers but they do nothing. any suggestions?