Coralife Pure Flo II Reverse Osmosis Micron Pre-Filter CartridgeMany contaminants that shorten the lifespan of your R/O membrane can be strained out through the use of a much lower cost pre-filter. These pre-filters are inexpensive and significantly improve the functional life of your R/O membrane. Maintenance/Lifespan: Micron pre-filters should be replaced every 3,000 gallons or 6 months (whichever occurs first). Depending on the quality of your water source, you may need to replace these pre-filters as often as once per month. If not replaced, certain elements (such as chlorine) will become present in your purified water and your membrane cartridge will also become damaged.