I would not add anything else yet. I would however bring the chlorine up to 10 - 12. You are fighting something because you have combined chlorine. I think if you take the chlorine up to 10 or 12 and leave the filter on 24/7, the water will clear. I don't have any experience with cartridge filters, as I have a sand one, so I don't know how long it will take to filter out what the chlorine has broken down. Take up your chlorine, and your POP, and I think it will do the trick.