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When filter media other than sand is employed, special requirements must be satisfied. The process involving filtration through a coating of filter-aid material such as diatomaceous earth on porous tubes or elements is satisfactory when the following conditions are met:
1. Sufficient element surface area is provided to filter the entire contents of the pool in six hours at the rate of 2 gallons or less per minute per square foot (7.57 lpm/0.09 m
2
).
2. Slurry feeding equipment is provided for the continuous application, at an accurate and uniform rate, of filter-aid material into the filter influent line.
Exception: Such feeders may be omitted at pools where filter-aid units have sufficient element surface area to filter the pool volume in six hours at a rate not to exceed 1 1/2 gallons per square foot (5.68 L/0.09 m2) per minute.
1. Pressure gauges are installed on both the influent and the effluent side of each filter unit.
2. A rate-of-flow indicator properly located and having satisfactory range is provided on the effluent line from the filters.
3. Sufficient head room and facilities are available in the filter room for periodic removal of the filter head and element assembly for manual cleaning purposes.