Cleaning your cartridge filter:

If the filter cartridge has a coating of Algae, calcium carbonate (residue from calcium hypochlorite), iron or any other minerals, soak the filter cartridge in a solution of one part muriatic acid to twenty parts water until the bubbling stops.   RINSE THOROUGHLY AFTER.  WARNING:  Failure to remove all oils and cleaning solutions could result in the permanent restriction of water flow through your cartridge filter resulting in a partial or complete failure of your cartridge filter.

If the filter cartridge is still dirty or has been used in a spa or swimming pool where oils like perspiration, sun tanning lotions/oils are frequently used, then soak the filter cartridge for at least one hour (overnight is more effective) in either A: a commercial filter cleaner, or B: in a solution of one cup of Trisodium Phosphate (TSP) to five gallons of water. or C: a solution of one cup of dishwashing liquid to five gallons of water.