Filter Turnover Rate

The calculation of the turnover rate most frequently used is simply: Volume of system in litres / Rate of pumping litres per minute = turnover time in minutes. Thus in an aquarium with a volume of 1000 litres and a pump rate producing 100 litres per minute, the result is 1000 / 100 = 10 minutes. However, that does not mean that in 10 minutes all the water in the aquarium has passed through the filter (pump) attached to it. It takes much longer to ensure that all the water has passed through the filter.

The explanation is that in the first minute 100 litres (10% of the total volume) of water passes through the filter. At the end of that minute the system contains 100 litres that has been through the filter and 900 litres which has not. Assuming there is good mixing in the next minute, 100 litres passes through the filter but 10% of this will already have passed through the filter. Thus at the end of two minutes 190 litres not 200 has been treated.

The formula to use to work out the time taken for all the water in the aquarium to pass through the filter (pump) is: Volume of system in litres / Rate of pumping litres per minute x 9 = time in minutes for all the water to pass through the filter. Thus in this example 1000/100 = 10x9 = 90 minutes. This is of course assuming there is sufficient mixing of the aquarium water. You can expect an even further decrease in flow rate from 10 to 50 percent once filter material is added.