I was told that during the winter, you do NOT want your air line to go all the way to the bottom of your pond, for it may super cool the water. Half way was what I was told. True?
There is a lot of misinformation on this aspect of aeration in a pond during the winter. Most of this information has been created by what people think should be done. Then it self-perpetuates because “it makes sense” to the unknowing. The idea gets incorporated into the mainstream literature without giving it a second thought. This concept may be true in very large ponds but not in backyard water gardens and Koi ponds.
I have carried out some experiments of where I placed the aeration point in a pond. The pond water temperature was the same at the bottom of the pond no matter where I place the aeration point as long it was in the center of the pond. This occurs for a very simple reason: water that is aerated from mid column (half way down into the water) creates a plume of water welling up from that point. This water goes to the top and then circulates to the sides of the pond and then to the BOTTOM. In our relatively small bodies of water any circulation ends up circulating the whole pond unless you have dead zones (inlets, coves and the like will create these). I WANT the whole pond circulated – I do not want any dead zones.
As for “super cooling” the water: the water gets very cold no matter what. In my experiments the water will get to 32.1°F on the bottom of a 5.5´ pond in a typical aerated Midwestern Koi pond in the middle of winter without
ANY loss of fish. I have lost fish when I have failed to add aeration on a timely basis. In this instance I did not get my aeration going until after a layer of ice had developed. I learned 20 some years ago to have aeration going as soon as the water starts to cool. For that matter, I now have aeration going year round. This is in addition to my waterfall/stream pumps. I need to say that these waterfall/stream pumps are shut down when heavy freezing occurs. I do this because it is way to risky. I do not want the stream to ice dam and overflow the sides. This can occur after a power outage where everything freezes or a chunk of ice breaks free in the stream and creates the ice dam.
I did say that I want to make sure that aeration is going as soon as the water starts to cool. If you start heavy aeration after the ice is already formed then you can possibly super cool a pond. The temperature can go from a relatively balmy 39°F to 32°F in a few minutes. This is pure conjecture on my part because I do not want to do this and jeopardize my fish or any of my clients’ fish.
I like to think of our ponds in a couple of different ways. First, a 3´ deep un-aerated pond that has a foot of ice on top of it – what do you think the temperature is of the water on the bottom? Remember the ice is only 2´ away from the bottom. You bet it is so close the temperature of the ice (32° F) that you could not tell the difference. Remember this is without any aeration. I have seen 2´ deep 1000 gal. aerated ponds that have 18˝ of ice except where the aeration is and the calico shubunkin goldfish survive it in great shape.
I would not want Koi in this situation only because there isn’t any space for them to swim.
Second, Midwestern streams in winter have heavy ice on them except where there is fast flowing water and the water is then exposed to the air. The entire stream water temperature is the same throughout the water column. All of our fish survive these conditions very well, even Carp. We all know where Koi were developed. Even though Koi are a distant relative of Carp I maintain that they are as hardy.
Please refer to the article that I wrote for POND Trade Magazine for more specifics – Overwintering Koi Under Thick Ice September/October 2009. (http://bit.ly/co7sRY)
I am working on some more info about overwintering fish under heavy icing conditions. Please stay tuned.
All in all – place that aeration point on the bottom of your pond, in the center.