The FilterLogic CT600 series is a polyphosphate dosing cartridge, designed for whole house scale control.
Designed to fit into a regular Ametek/Pentek style housing, this cartridge doses the water with a tiny amount of food-grade scale inhibitor which prevents calcium and magnesium ions from bonding together and forming crystals.
Whilst not a true 'water softener', dosing systems such as this prevent damage caused by limescale to appliances such as combination boilers, kettles, steam irons and steam ovens. In addition, water marks caused by limescale in baths, showers and toilets are significantly easier to clean, with limescale forming a light powdered finish which doesn't adhere to surfaces strongly.
This cartridge, in a typical household installation, should last approximately six months.