When I started my KOI pond, I was like everyone else and knew very little except of course for what I read in several books. One of the lessons learned is that using an air pump used to aerate the pond during the winter can aid the survival of the KOI.
Brief Background. When I built the pond, I constructed three ponds with waterfalls connecting each pond. There is roughly a four foot drop from the upper pond to the lower pond. There are three design criteria that are critical for this discussion. First, when I shut the pond down for winter, usually some time in November, I reduce the effective volume of the ponds by roughly one third. Next, when the pond is shut down and the waterfalls cease to flow, there is no longer active oxygenation of the water. Last, the pond is four feet at its deepest point. The frost line in our area is eighteen inches. The pond would not freeze solid and based on my research, the fish should survive the winter. (Figure 1)
The First Winters. Summarizing my readings on winterizing are as follows. Avoid vibration because this can kill the fish. Creating a hole in the ice with a heater allows the gasses to escape. Overall, the circular heaters were slightly less than satisfactory. They tended to breakdown, and when they did it was difficult to determine whether the cold weather overwhelmed them or whether they simply ceases to work. Also, after a good snow storm, the snow would need to be cleared.
For me, this approach worked for about four years and then I found my fish frozen dead in the ice. I did this once again and after four years found my fish dead in the ice. The following were my conclusions at the time.
- When my fish were small, they could survive the winter. There was sufficient oxygen in the water for them to survive.
- My fish reached a size where my small pond could no longer support them during the winter.
- In small ponds with large fish, the heater method of winterizing simply won’t work.
Rethinking the Situation. Long term, it was clear that my current setup wasn’t working. Cutting to the chase, I wondered if there was any difference between my pond and a small fish aquarium with a small air pump to aerate the water. The simple answer is that there isn’t.
How a Pond Freezes. Water is unique when it freezes. Unlike most materials, water expands when it freezes rather than shrinks (Figure2). In a global sense, this prevents the oceans from becoming a solid ice cube. When water cools to 36 degrees Fahrenheit, the water molecules begin to slow down and realign themselves into an hexagon. This occurs because the two hydrogen atoms do not line up on opposite sides of the oxygen atom. The result is that ice is less dense than water and it is the reason why ice floats.
Other than being a serious sidebar on why ice floats, I had significant concerns with pumping air into my pond. A lot of it stemmed from the literature on the heaters. There is a temperature differential between the surface and the bottom. The result are convection currents. The water on the surface is being cooled by the cold air. In contrast, the water on the bottom or four feet deep is being heated by the ground which is generally at a temperature of 55 degrees Fahrenheit. The water on the bottom may be colder than 55 degrees Fahrenheit (Note: I never measured it), but it is warmer than the water on the surface. This is the reason that the KOI sit on the bottom in the warmer cold water. Conversely, when the KOI swim close to the surface in summer, they are seeking the warm water on the surface being heated by the sun or localized air. Meanwhile the ground is attempting to cool the water on the bottom.
My fear was that by pumping air to the bottom of the pond it would create a convection current that would mix the water and tend to equalize the temperature of the water and harm the KOI. There was some trepidation during the first winter where we had temperatures going below zero degrees Fahrenheit. As a footnote, one source discussing air pumps suggests not putting the outlet on the bottom. I note this but I didn’t have a problem doing so. I should also note that the deeper the air pump outlet is placed, the more difficult it is for the air pump to overcome the water pressure.
Typhoon Air Pump. Not knowing much about air pumps, I purchased the Typhoon Air Pump roughly ten years ago. (Figure 3) I believe that my model has been discontinued and replaced with an updated version. Regardless, the repair kits containing diaphragms and valves are still available.
Having become well versed on the Typhoon Air Pump, these are my comments on the pump. It is a simple well designed pump that is dependable. The diaphragms and valves last about a year so buy one or two replacement kits. They cost roughly $24. A Philips screwdriver is all that is needed to replace the diaphragms and valves. It is not difficult. I will note that the air pump is well engineered. You cannot reassemble the parts incorrectly. They interlock together in only the correct way. It is good engineering. As I write this, the outside temperature is 15 degrees and the pump is humming away.
Every pond is different. So what I did is illustrative. I installed the Typhoon air pump outside in a small structure which also contains a bio-filter. (Figure 4) This keeps the air pump dry and out of the weather. I do not use it during the summer, but if I shut down the recirculating waterfalls, I can simply plug it in, everything is ready to go. The air pump outlet is close to four feet underneath the water and is normally at the bottom of the pond. There is another two feet elevation to the pump and the total hose length is a fifteen to twenty feet in length. The pump is happy and the water is aerated.
KOI Behavior. It is interesting to watch the behavior of the KOI. When the air pump is on, they align themselves in formation on the bottom generally facing the outlet of the air pump. If I turn the pump off, they realign themselves on the bottom at a different angle. When I turn the pump on again, they realign themselves back to their original formation. In their semi-hibernation, they seem to be still maximizing their efficiency by minimizing their loss of energy.
Before the last rebuild of the air pump, it was limping along so I raised the outlet off the bottom. Again, the fish changed their behavior and some of them moved to the shallower area to be in close proximity to the aerator. I suspect that they were seeking the more oxygenated water.
In Conclusion. For my KOI pond, it has been a somewhat serpentine route to the eventual use of air pumps to aerate the water in winter. Hopefully, others will find this information useful. In summary:
- Consider installing an air pump as part of winterizing your pond. Think of your pond as a big aquarium located outside. My experience over ten years is testimony to their success. My KOI are now over 24″ in length, and that presents a different problem. My fish are now too large for the pond. However, they are surviving the winter.
- I am not a fan of the heaters. They don’t work well with large KOI in small ponds. If they installed a small diode light, you will visually know when it is operating.
- Depending on circumstances, I winterize and shut down the pond in the second or third week in November and reopen it in March. For roughly three months, my pond is utilizing the air pump to aerate the water.
- Purchase a good air pump. Install it in a dry location.
- Although some don’t recommend placing the air outlet on the bottom of the pond, I haven’t experienced any problems yet. It is your choice.
- If the pump uses replaceable diaphragms and valves, consider purchasing extra repair kits. Without aeration of the water in the pond, my fish will go no more than two days at most before they become noticeably sluggish. Having the repair kits on hand is prudent.
