Filter media for use in pool filters

1. A sand filter for use with swimming pools comprising:

a tank that has a hollow interior space;

a top diffuser for allowing spent pool water to enter the tank and for distributing the pool water inside the tank;

filter media formed as a bed of material on a bottom of the tank; and

laterals that are located under the filter media and allow filtered pool water to exit the tank and flow back to the pool;

wherein the filter media includes a bed of sand that is disposed on the bottom of the tank and a layer of perlite material that is disposed on a top surface of the bed of sand, the perlite material being a high flow rate, low density perlite material that only contains a trace amount of floaters.

2. The sand filter of claim 1 , wherein the perlite material has a specific gravity of about 2.3; a wet apparent density between about 8.5 to 9.5 lbs/cubic foot; a loose weight density between about 5.5 to 6.5 lbs/cubic foot; and a Darcy units of about 3.25.

3. The sand filter of claim 1 , wherein a weight of the perlite material is about 0.25 lbs/ft 2 .

4. The sand filter of claim 1 , wherein the layer of perlite material comprises a cake structure of perlite material.

5. A method of at least substantially eliminating Cryptosporidium organisms from pool water comprising the steps of:

passing pool water through a sand filter to generate filtered pool water, wherein the sand filter includes a filter media comprising a bed of sand that is disposed on a bottom of a tank of the filter and a layer of perlite material that is disposed on a top surface of the bed of sand, the perlite material being a high flow rate, low density perlite material that only contains a trace amount of floaters.

6. The method of claim 5 , wherein the perlite material is added in an amount of ¼ lb per sq. ft. of filter surface area.

7. The method of claim 5 , wherein the filtered water is at least 98% free of the Cryptosporidium organisms.

8. The method of claim 5 , wherein between about 97% and about 99% of the Cryptosporidium organisms are removed from the filtered water by passing the pool water through the sand filter.

9. A method of forming a sand/perlite layered filter media in a sand filter that is part of a swimming pool that includes a skimmer, comprising the steps of:

adding sand to the bottom of a tank of the sand filter to form a bed of sand;

operating the sand filter so that water passes therethrough; and

adding a predetermined amount of perlite material through an inlet of the skimmer that is in communication with pool water, while the sand filter is operating, resulting in the perlite material being added as a layer to a top surface of the bed of sand.

10. The method of claim 9 , wherein the perlite material is a high flow rate, low density perlite material that only contains a trace amount of floaters.

11. The method of claim 9 , wherein the perlite material has a specific gravity of about 2.3; a wet apparent density between about 8.5 to 9.5 lbs/cubic foot; a loose weight density between about 5.5 to 6.5 lbs/cubic foot; and a Darcy units of about 3.25.

12. The method of claim 9 , wherein a weight of the perlite material is about 0.25 lbs/ft 2 .

13. The method of claim 9 , wherein the layer of perlite material comprises a cake structure of perlite material.

14. The method of claim 9 , wherein the perlite material is prepackaged in a package that includes a label that equates the amount of perlite material in the package to a square footage of the filter.