Yesterday we discussed a few testing and removal options for nitrates. Today we’d like to address an issue brought to our attention by several readers: nitrate filters for existing filter housings.

A good number of water filter companies have started using one of several common sizes (20″x2.5″, 10″x2.5″, 20″x4.5″, 10″x4.5″) for their housings in an effort to standardize product lines between manufacturers and give consumers more filtering options once they own a particular type of filter system.

Many people refer to those sizes as ‘big blue’ sizes since at one time, and still to this day, a very popular brand of water filter (Pentek) manufactured its products using blue polypropylene.

Filter Water: 20 x 4.5 Inch Big Blue Filter
20″ x 4.5″ Big Blue Filter Housing

Filter Water: 10 x 4.5 Inch Big Blue Filter Housing
10″ x 4.5″ Big Blue Filter Housing

Now that you know a bit more about filter housing sizes, and hopefully have figured out the correct size cartridge for the unit you own, below you will find several replacement nitrate filter cartridge options:

Filter Water: Multistage Nitrate Filter
Multistage Nitrate Filter

Filter Water: Replacement Nitrate Filter Cartridge
Nitrate Filter Cartridge

Filter Water: 20-Inch Nitrate Filter Cartridge
20-Inch Nitrate Filter