Average Turnover Rate
The average turnover rate of pond water should be in the range of 1 to 3 times per hour. The turnover rate is defined as the number of times the total volume of pond water flows through filtration in one hour.
How often the water is turned over is dependent on; the pond size – a smaller pond benefits from greater turnover; the type and population of fish in the pond; the amount of aeration of the pond – oxygen is your friend; and the type of filter.
Smaller ponds need a higher turnover rate than larger ponds. Things happen faster in a small pond, and smaller ponds are usually more likely to be overstocked. Small ponds are also less stable, as their temperature fluctuates more. This means that a <6000 litre pond will benefit from a higher turnover rate of about 2- 2.5 times per hour.
The turnover does not generally include water that is bypassed directly back to the pond past the filtration system. Although this is a little bit of a grey area, because some bypass water can be used for very useful purposes: e.g. current flow, and aeration such as a waterfall or fountain.
Filters separate out debris and silt, however also provide the surface area for aerobic bacteria
Typically my larger ponds (>6000 litre) should be run approximately 1.5 times per hour, through filtration.
Extremely large ponds and small lakes can run much lower rates and the rules apply much differently. The higher the dissolved oxygen content, the lower the turnover rate can be. Oxygen is your friend.
You can also use our handy online calculators to determine your requisite pond volume and litres per hour, here.