BritinUSA:

I congratulate you: You are the first person I've come across who is happy with their Nature2 system! Seriously. Most hate it or have problems they didn't realize was related to it.

But I believe N2 recommends you change the cartridge every 6 months or every season, which ever it shorter. You are using yours for 2 seasons so you have ALREADY cut your costs in half by breaking "the rules" --not that you shouldn't--if you have been successful with 2 seasons per cart you've already gotten ahead of one of the objections to the N2 system.

How about posting your test numbers, along with your pool size and type (vinyl, concrete, in-ground or above ground)? It would be interesting to see what works with Nature2. Perhaps we'll be able to recommend ways for people to be successful with them. Currently we do NOT recommend Nature2 under any circumstances.