When the filtered water tastes acidic or fishy the filter has reached the point of exhaustion and must be replaced. Filter life depends on your household water consumption and the amount of TDS (total dissolved solids) in your tap water (water chemistry varies by source and how it’s treated locally by your town or municipality). Please refer to the tds chart to determine how many gallons you will get per filter. It is important that you periodically test your filtered water with your water quality meter and when the meter reads 006 or higher the filter should be replaced.