Slow-Start to Prevent Pond Turnover & Fish Kills

Prevent Pond Turnover

Mid-summer is often the time of year when oxygen demand in your pond is at its greatest. Once a pond or lake has had several months of warm summer temperatures, it has most likely established a strong stratification. This is also known as the layering of water by temperature and density. At the surface is the warm, less dense water and at the bottom is the cold, denser water. The area in-between these two densities is known as the thermocline.

Stratification can make it potentially dangerous to use a bottom aeration device, such as our Robust-Aire Diffused Aeration Systems. This is due to the rapid removal of the density barrier. Robust-Aire works by pumping air through weighted tubing to the diffuser on the bottom of the pond or lake. As the bubbles rise, they carry large volumes of water to the surface. This mixes the full water column and allows for uniform temperature and oxygen levels.

Kasco Robust-Aire™ Systems

The Consequences of Rapid Mixing

If a system is turned on and left to run continuously, it will quickly eliminate the density barrier and stratification. Ultimately, this will lead to the entire pond or lake being of consistent temperature and improved oxygen levels. Most of the time, this is a good thing. However, if the layer of cold, bottom water is much larger than the area of top, warm water, it could create a pond turnover very rapidly.

A pond turnover is the rapid mixing of water. This can often be followed by a fish kill as a result. The water at the bottom is virtually void of oxygen and filled with potentially harmful gases, whereas the surface water is full of oxygen. Mixing the two together creates an entire water column of low oxygen. Consequently, if the oxygen levels get too low, fish can die.

Consequences of Rapid Mixing

The Slow-Start Procedure

To avoid a pond turnover and fish kill, Kasco clearly outlines a “Slow-Start” procedure in our Robust-Aire Owner’s Manual. This procedure consists of running the equipment for shorter periods of time, gradually increasing the run time over a period of a couple weeks. Doing so will ensure the pond or lake is able to mix and react slowly to the added aeration and circulation, preventing a fish kill.

If you have already turned your diffused aeration system on and are experiencing a rapid pond turnover or notice fish “piping” at the surface, turn the system off. Instead, try to add supplemental aeration at the surface quickly, such as one of our Surface Aerators. In a pinch, even a trolling motor, boat motor, or sump pump splashing at the surface can help. Once the danger of a fish kill has passed, you can turn the Robust-Aire system back on and follow the slow-start procedure.

Kasco Surface Aerator

If you have any questions, please email us or call 715-262-4488.


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