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Prevent Fall Turnover & Fish Kills by Using Aeration – Pond & Lake Q & A

Picture of a Fish Kill due to Fall Turnover

Being Aware of Fall Turnover.

Instead of a Q & A for Ponds & Lakes today, I wanted to make everyone aware of what Fall Turnover is and the steps you can take to protect your fish. Around this time of the year we receive quite a few phone calls from customers waking up to find a pond full of dead fish. Hopefully, I can shed some light on this subject that can help you prevent an event like this from happening.

What is Turnover? With no aeration present, the pond’s water is stratified (aka has a thermocline). Meaning that the water at the top is warmer and full of oxygen while on the bottom the water is cooler, nutrient rich and contains no oxygen. This causes the fish to habitate towards the surface of the pond. As the seasons change from the hot summer to the cold winter, the pond goes through a process known as “turnover”. This is when the cooler,
un-oxygenated water at the bottom of the pond, mixes with the warmer oxygenated water at the pond’s surface. Since the rising cooler water contains no oxygen, the fish lose the ability to breathe in a sufficient supply of oxygen. Shortly after, the fish begin to die.

Aeration to the Rescue! You’ve probably heard me talk about aeration in many Q & A’s over the past couple months and are probably sick of hearing about it. But it really is that important and really is a solution to a majority of a pond’s problems.

By properly aerating your pond, the oxygen will be saturated throughout the pond, thus eliminating the thermocline and eliminating the chance for future fish kills caused by “turnover”.

You can also under-aerate a pond as well. Please read the following Q & A for more information.

2 Responses

  1. Lenore Castaldo,

    You can absolutely use de-icing units to keep a hole open in the ice.

    As for the aeration system, you are correct when it comes to mentioning that fish like still water during the winter. My suggestion (and I forgot to put it in the blog post) is to place the aeration system away from the deepest point during the winter. I would place it closer to the edge of the water garden. This will still allow for aeration as well as keep a hole open in the ice.

    What I’ve done many times is place the small bubbler system underneath the de-icer itself to ensure that a hole is always open.

    Thanks for your comment Lenore!

  2. Although you reccomend leaving the aeration on for for winter, I read somewhere that doing so will cause the fish to be unable to be still and that they will have to use their energy trying to “hibernate”, instead of remaining still.

    I was intending to turn off the aeration when the pond water reached 39 degress and put in 2 de-icing units.

    What is your thought on this info.?


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