The Aquatic Life twist-in 100 gpd 4-stage reverse osmosis deionization system is a very compact water purification solution that efficiently combines reverse osmosis and deionization technology with our quick and easy to change twist-in replacement filter cartridges. The new twist-in media cartridge design makes filter changes simple, easy and clean no tools required and no mess! the twist-in cartridges can be easily changed in seconds with just a quarter turn and without contact with used filter material, and the supply water to the unit does not have to be turned off to replace any cartridge. Stage 1 sediment filter: replace every 6 months. The First stage of your reverse osmosis deionization unit is a 5-micron sediment filter that traps sediment and other particulate matter like dirt, silt and rust which will affect the taste and appearance of your water. Stage 2 carbon block filter: replace every 6 months. The second stage of your reverse osmosis deionization unit is a carbon block filter. The Activated carbon in the filter reduces chlorine by 99% and conditions the water prior to the membrane. Stage 3 membrane: replace every 1-2 years. The reverse osmosis membrane reduces impurities known as total dissolved solids from the water down to 1/10,000 of a micron, reducing arsenic, lead, parasitic cysts, COPPER and more. Stage 4 color changing mixed bed resin: replace filter when resin changes color to amber. After the water is filtered by the membrane, there is usually a small amount of total dissolved solids left in the water. In certain non-drinking water applications it is important to remove the remaining tds from the water. This is accomplished by filtering the water through a resin that is charged with cation and anion resins (H+ and oh-). as the resin absorbs the tds it will change color. When all resin has changed color it is time to replace the resin cartridge. Assembled product Dimensions: 13 wide x 4 deep x 13 high. Weight: 7 lbs.