Our 6 pack of water fountain filters offer you long term usage, and each filter is well-sealed and individual packaged. Adopt activated carbon, premium cotton and premium ion resin, effectively solve hair, debris, harmful microorganism and excessive ions problems. Filter need to be replaced every 2-4 weeks and more frequent replacement is required if multiple pets exist. Fit for 2.5L/84.5oz pet water fountain(GPCT4135) sold in our online store.