If the surface of the pond freezes completely over,
the fish die from carbon dioxide and ammonia poisoning.
A large quantity of water for a small proportion of koi
acts as a buffer because it takes longer for the water to saturate
with toxins. This gives you a very little bit of time to open the
surface of the pond before the fish die. A small pond with a large
quantity of koi that freezes over will kill the fish within hours.
This is another very strong argument for minimizing the population
in the fall.
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How much surface needs to stay open? Very little. A 3 inch hole
in the surface ice will allow for adequate gas exchange for most ponds.
Carbon dioxide out, oxygen in. This is a natural cycle that will
happen automatically as long as there is a hole somewhere in the surface
for the gasses to exchange.
How is a hole kept open? There are many devices on the market, but
the key concept is to keep the de-icing equipment at the surface
of the pond. As discussed earlier, do NOT put any
device that will circulate water in the bottom of the pond.
Rig the devices to a support or float of some sort so they stay
put at the surface.
What devices? In Minnesota it is recommended that a heating element
is used in conjunction with an oxygenating source. When looking at
oxygenating sources, or air pumps, look for
piston driven linear air pumps. Do NOT use an aquarium
air bubbler. The diaphrams are not designed to withstand Minnesota's
extreme minus temperatures. They WILL crack and fail. Linear air pumps
cost from $70 to a couple hundred dollars each. When looking at heating
elements, look at wattage. Livestock stock tank heaters are readily
available in most areas, but why pay to run 2500 watts when 150 watt
floating pond heaters are available for less than $100? Most come
in a floating donut shape that keeps the center 3 inches from freezing.
Mike from Koi Acres claims that one 120 watt Pondmaster floating
heater (which they carry) is enough to keep fish alive in their 93,000 gallon
display pond! Keep in mind, however, that the manufacturer rates
the heater for a 2,000 gallon pond.
IMPORTANT UPDATE:
In a recent discussion with Mike from Koi Acres,
Mike has concluded that the 150 watt floating donut heaters do NOT withstand our Minnesota winters. He claims
that they have a high failure rate and there is a good chance that they may NOT last the winter without shorting
out. PLEASE keep this in mind and never rely upon these donut heaters as the sole means of de-icing your pond, and
by all means make sure you are plugging into a GFI protected outlet. The donuts are a good, inexpensive tool for
casual koi ponds, but if you value your herd, use with CAUTION!
My pond has a floating 1500 watt stock tank heater with protective guard for the 2007/2008 winter. Used alone,
my fish started coming to the surface, nose up. This was a clear sign of oxygen depletion. Unhealthy in itself, the fish
were also in risk of gill damage by being forced up into the colder 32 degree surface water. To remedy this situation
I have repositioned the pond pump into a 12" deep "spawning cove" well away from the resting
koi. It is pumping water into the air about 5" high causing sufficient oxygenation via surface disruption that the
fish have returned to their resting deep zone. Our coldest temperature thus far in the 2007/2008 season has been between 0 to 5 degrees F and
this combination seems to be working good, keeping the surface open, keeping the water oxygenated, and keeping the deep water at 42 degrees F.
I've used an aquarium powerhead tied to a plastic milk crate, pointing
upwards for awhile but there are some cautions to this method. Water
tends to travel, and sometimes the powerhead (or any pump for that matter)
will pump the water onto the surface of the ice instead of back into
the pond. This may cause the pump to lower the pond level enough to
burn out the pump. Another thing that happens is that an ice dome
may form over the pump causing the surface to freeze over.
When placing your de-icing devices, place them in an area away from where
the koi are resting in dormancy and where the devices can be reached.
This allows for easy check-up and maintenance of the devices and also
makes it easy to open the frozen hole in case of a power outage.
In the case of a power outage, act quickly and frequently
during the outage.
CAUTION: Do NOT bang on the ice to open a hole!
Koi are extremely sensitive to vibrations. Sensors
along their lateral lines pick up even the faintest vibrations
and can be compared (loosely) to human eardrums.
Imagine you are deep asleep at 3:00am and somebody bangs on a steel
garbage can as loudly as they can right next to your pillow. This
is the sensation created when trying to chip out a hole in frozen ice.
When re-opening the hole, work as delicately and quickly as possible.
Hot water can be used, but extreme caution must be used to prevent
any of the hot water from entering the pond. The goal is to open the
hole without disrupting the stabilized pond temperatures and without
stressing the koi. The hot water method is another good reason to
keep the de-icing devices away from the koi, just in case some hot
water enters the pond.
Remember, if winter koi outdoors, in the elements,
in Minnesota, at some point you will probably lose some fish.
Understanding and applying the concepts presented on these pages will
ensure a greater success rate of over-wintering your koi in Minnesota's
extreme cold weather.
