There have been several discussions lately on social media regarding reverse osmosis system pre-filter cartridges and micron ratings. We would like to jump into the discussion with information we think will help explain the purpose of sediment and carbon pre-filters in RO and RO/DI systems and what the various micron ratings mean. Here goes...

The purpose for Sediment and Carbon pre-filter cartridges is to remove particulate and chemicals such as silt, rust, sand, chlorine, etc. These cartridges have a micron rating. The micron refers to the size of the pores in the cartridge. The larger the rating or number, the larger the pore size in the cartridge. Cartridges are often rated 10, 5, 1 and even 0.5 micron. The smaller the number, the smaller the particulate removed from the water. It seems logical at first to use the smallest micron filter to remove the most amount of particulate. However, this is not always good in practice for several reasons. First, the cartridges could plug quickly and you will need to replace the cartridges often. In addition, a plugged or restrictive cartridge means not as much water flows to the membrane and the membrane needs adequate water pressure to function properly. For this reason, most RO Membrane manufacturers recommend a maximum of 5 SDI rating for the water supply to allow the RO Membrane to do its job properly. This is typically done with filter cartridges using at least 5 microns for first stage filtration on the RO units.

The Aquatic Life Sediment and Carbon pre-filter cartridges have a 5-micron rating designed to work efficiently and effectively with the RO Membranes. Keep in mind the Membrane is the heart of any RO filtration. Most Membranes (and all Aquatic Life Membranes) will last longer if they are “flushed” periodically. This involves adding a simple Flush Valve, allowing water to bypass the Flow Restrictor on the RO unit.

In summary, using a smaller micron rated pre-filter will trap more sediment, but if not changed often will diminish the effectiveness of the RO Membrane and Membrane manufacturers recommend using an appropriately rated pre-filter.