Welcome to our forum.
Checking in to represent the west side, with a Happy New Year from Plymouth!My water is only six weeks old, but Kervis' post got me thinking that I should consider at least a partial drain and fill this weekend, so I'm not worrying about stretching the water to late March. The only problem is the Nature2, and the amount of time and acid it takes to balance my water.
My Nature2 was only 2 months old, so I just took it out, waited a couple hours to let the Defender do it's work, then I stuck it back in, added dichlor, and we'll see what happens!
It has been awhile since I looked into N2, but my understanding is that the all the silver and copper ions are released into the tub in the first couple of weeks, and they just stay in solution until the water is changed. I may have this wrong, but I don't think there is anything left in your cartridge at this point. I'm guessing that the 4 month life they talk about is based on an assumption that most water is changed on a 3-4 month schedule. You mentioned not using Metal-gon this time. I have tried Metal-gon, SeaKlear clarifier (which used to claim to remove metals), and nothing. I found that Metal-gon and SeaKlear captured a light amount of iron and deposited it on the filters where it was easily rinsed off, while using nothing resulted in the same amount of iron deposits -- but not until the first shock, and bound to the filter in a way that didn't rinse off. Now, I just use the SeaKlear at fill, and as a maintenance item alternated with Defender on a weekly basis. That has been working well.