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A while back I was wondering if I changed or even partially changed out the water before the 4 months can I keep using the N2 cartriidge. This is what the N2 folks said"You will need to replace the Nature 2 whenever the water is drained and refilled. This is because you loose a good percentage of the silver ions when you drain the spa, and their is not enough in a depleted cartridge tobring it back up to the proper level. So you will need to change the Nature 2 cartridge."My guess is if you change out 1/2 the water you will need to change the N2 cartiridge as well. Nice to know someone has the same problem after 2 months.Rick
...I shocked and didn't use it for 4 days. On the 4th day it was a LITTLE cloudy so I schocked it with the normal 4 Tbls. The next day it wes still cloudy and no Cl on the test strip. I reshocked with 4 tbls and the next day again still a LITTLR cloudy and no Cl on the strips. I then shocked with 8 Tbls and after 40 hrs it wss clear but again no chloriine on the strips. ... So why is it taking so much chlorine?