Filter to provide clean water to my refrigerator drinking water and ice dispenser.

I would like to install a filter to provide clean water to my refrigerator drinking water and ice dispenser. The filter would be located in the basement, connected directly to the refrigerator supply line in a closet. I would like it to be large enough so it would not require service more than about once a year. The water is from a private well, softened before it gets to the refrigerator. I am mainly concerned about nitrates, which recently tested at 11 ppm. Which of your products should I be considering?
If nitrates is your primary concern we carry A-3I nitrate Imperial cartridge which can be found on the following page. The 10" filter housing can also be found on the same link: http://www.doultonusa.com/HTML%20pages/ceramic_cartridges.htm