I was using the Sundance nature 2 cartridge and MPS/Chlorine since my tub was new in June, and I found if I went more than 2 days after adding chlorine I was greeted by a cloudy tub. The last straw was over the holidays when it was 10 degrees and snowy, so I didn't think about going out there to add chlorine, and I came out to a cloudy tub. I don't know what the Nature 2 cartridge was doing for me, but it seems after 2 months I get no benefit from it, and must add chlorine daily to keep it it clear.
The Monday following Christmas, I made the switch to Bromine. My tub has a bromine dispenser in the weir gate, so I followed instructions found elsewhere here and I'm happier. I checked the levels daily for over a week and I'm now confident to add bromine tabs to the dispenser and shock it once a week.