Pool Filter Turnover Rate

The number of times a pool’s contents can be filtered though its filtration equipment in a 24-hour period is the turnover rate of the pool. Because the filtered water is diluted with the nonfiltered water of the pool, the turbidity continually decreases. Once the pool water has reached equilibrium with the sources of contamination, a 6-hour turnover rate will result in 98% clarification if the pool is properly designed. A typical-use pool should have a pump and filtration system capable of pumping the entire contents of the pool though the filters every 6 hours. To determine compliance with this 6-hour turnover standard, the following formula is used:

Turnover rate = pool volume (gallons)/flow rate x 60 (minutes in hour)

Following is a sample calculation of the pool content turnover rate using the rate of flow reading from the flow meter:

Turnover rate = 90,000 (gallons in pool)/180 gallons per minute x 60 (minutes in hour)

8.3-hour turnover rate = 90,000 (pool volume in gallons)/10,800

The above pool would not meet the required turnover rate of 6 hours. The cause could be improperly sized piping or restrictions in the piping, an undersized pump, or undersized or clogged filters. This turnover rate would probably result in cloudy water if the pool is used at the normal bather load. The decreased circulation would also make it difficult for the disinfecting equipment to meet the required levels.