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Introduction:
Minnesota has some extreme weather conditions
that call for special measures when trying to overwinter koi outdoors.
This article is written with the assumption that your pond is deeper
than the frost level in your area. With MN temps dipping into the
-40°F range, the frost level can be 4 feet deep or more.
A pond with an area 5 feet or deeper is the most reliable depth of a
pond for over-wintering koi in MN.
Koi ponds shallower than 4 feet can be over-wintered but the risk of
death and gill damage becomes greater, and the ability to keep the
pond from freezing solid becomes more difficult and expensive.
If you are just starting out, do yourself a huge favor and put a
deep area in your new pond!
So, how can your koi be over-wintered safely? Read on.
1) Minimize Population:
Do you have too many fish to over-winter?
Consider this... ...during the winter in an overstocked koi pond, generally speaking,
the largest, most expensive specimen fish dies first,
then the next largest, and the next.
Big dead bodies in the pond create excessive toxic ammonia
and more fish continue to die. By springtime only a handful of the smallest,
hardiest fish are left.
Again, do you have too many fish to over-winter?
How many koi can I have in my pond?
A healthy pond with adequate or (better yet) excessive filtration can only hold a limited
number of fish before health issues start arising. The general rule of thumb
is that one 24" koi needs about 1,000 gallons to live comfortably.
Smaller fish require
less space. A 12" koi would be comfortable in about 100 gallons, but next year there will
be overcrowding issues.
When evaluating the population of your herd, you'll have to decide if you want to keep
a couple larger specimens, or keep more smaller fish, or just risk it and see what happens.
In 2006 my winter pond was minimized to a couple medium quality mid-sized koi and a couple large
goldfish. Two 15" koi were donated to the Koi Konnection
(ask me) where they found a 25,000 gallon
pond to live in, a bunch of small koi, goldfish, and hybrids were stripped from the pond and
brought into basement aquariums, and my especially nice 18" koi was brought indoors to
winter in a heavily filtered stock tank with a few 6 inchers and my grand-daddy 10" goldfish
to keep him company.
You ask, "How many gallons are in my pond?"
Square/Rectangular Ponds:
In US Feet: Length X Width X Average Water Depth X 7.5 = US Gallons
In Meters: Length X Width X Average Water Depth X 1,000 = Litres
Round Ponds:
In US Feet: Diameter X Diameter X Average Water Depth X 5.9 = US Gallons
In Meters: Diameter X Diameter X Average Water Depth X 790 = Litres
Irregular Shaped Ponds:
In US Feet: Long Diameter X Short Diameter X Average Water Depth X 5.9 = US Gallons
In Meters: Long Diameter X Short Diameter X Average Water Depth X 790 = Litres
These formulas only provide a rough estimate of your pond gallonage. Due to slopes, varying
bottom grades, rocks and decorations, etc., these formulas will always be inaccurate and
should NEVER be used when measuring medication dosages. The ONLY true way to determine
your pond gallonage is to completely drain it (including all filter chambers and plumbing)
and refill the pond with a flow meter attached to your inlet.
2) NO Feeding:
As pond water drops below 50°F a
koi's digestive and immune system begins to slow down.
Their ability
to digest fish meal based foods begins to weaken. As water temps
fall less and less of the food gets digested and starts to build
up and rot inside of the fish.
The water at the bottom
of the pond is water you want to monitor.
60° is a good trigger temp to switch from fish meal foods to
a wheat germ based 'winter' food. It is easier to digest as the
koi are slowing down and will help
to prevent the fish from using up their fat reserves before winter
arrives. An alternative to commercial wheat germ foods is a pearl barley
with garlic (not garlic salt.) Pearl barley is very easy to digest and the koi absolutely
love garlic. If your koi have never tasted garlic, give them a tiny pinch
of it to see how they react. Mine went ballistic and then were surprised
by the flavor, spitting it out and taking it back in, ultimately coming
back to look for more. Garlic is also great for fighting off tapeworms and
internal parasites in mammals. I haven't been able to find a reliable reference
that says it applies to koi as well, but it can't hurt.
In 2006 I was still feeding Cheerios as a winter food but learned that
oats aren't as easily digested as pearl barley, and even worse is the list of
sugars and chemical ingredients in Cheerios. No longer recommended by plantkingdom.com.
Read here for a correspondence between me (Perry) and Sue Emerick, 2007 President of the
Upper Midwest Koi Club concerning Cheerios.
Many experienced koi hobbyists stop feeding when bottom water temps drop below 50°. Never feed or disturb the koi
during this period because the pond and the koi are stabilizing for the winter. This may seem early, but keep in mind
that the koi can pick at the algae slime layer in the pond, that the biological filter has started going dormant,
and that excess ammonia is far more dangerous than hungry fish.
Ammonia build-up is another reason to stop feeding.
At some point
you will probably be shutting down your waterfalls and filtration
systems. A dormant fish produces very little waste material and the
filter isn't needed. Running a filter system IMPROPERLY during the
winter can actually do more harm to your fish than good. (More about
that in other sections.) If you do shut down your pump system, this
would be a good time to cut back on feeding drastically so as not
to produce large amounts of ammonia.
3) NO Leaves/Debris, Clean Bottom:
Remove all leaves and debris from
the bottom of the koi pond.
Repeat: Remove all leaves and debris from the bottom of the koi pond.
Leaves and debris in the bottom break down quickly and ammonia levels
will sky rocket. Leaves also release tannins into the water which
not only turn the water a brown coffee color but will also mess
with the water pH. As if this isn't bad enough, the debris can also
be a potential hiding place for parasites and harmful bacteria that
can attack koi when their immune systems are at their weekest, both
in late fall and early spring.
Water garden enthusiasts might argue that this debris is beneficial
for the roots of water plants, but it is absolutely detrimental
to the health of any fish in the pond. Remove it.
In the fall, as trees begin to change color, pump out the water and
remove any plant matter. Do NOT scrub the
pond clean, the algae slime layer on everything provides late season
food while the koi are going dormant and may be beneficial to the
production of the koi's slime coat. The primary
purpose of the fall cleaning is to remove the heavy debris and leaves,
not sanitize the pond.
When the pond is cleaned and refilled, a leaf catching net should be
spread over the pond to keep new leaves from entering. Periodic
emptying of the net should be done to protect the netting and also
to keep the leaves from touching the water's surface. I leave my netting
in place until the ice has started to form on the water. By this time
most of the leaves have been raked up, blown away, or are frozen in place
in the garden. Some people leave the nets up all winter. I prefer
removing them because it has done its job and to preserve it for
another year's use.
4) NO Water Motion in Deepest Point of Pond:
Koi go dormant in
the deepest, densest part of the pond where the water temperature
stays 39°F. DO NOT DISTURB THIS WATER! It is
absolutely imperative that this naturally warm, dense water stays at
the bottom of the pond. DO NOT put a
circulating pump at the bottom of the pond to keep the surface from
freezing over. DO NOT put an airstone or
bubbler at the bottom of the pond. DO NOT
keep the waterfalls flowing.
All of these things could create a condition known as
SUPERCHILLED WATER. In temperatures below 32° ice starts
to form on still water. Moving water does not freeze, but is still
at or below the freezing point of 32°. This superchilled water
has individual molecules that have frozen into microscopic ice crystals.
As soon as this superchilled water stops moving the microscopic
ice crystals allow the water to freeze solid almost instantly.
If the naturally insulated dense water at the bottom of the pond
is disrupted and becomes superchilled the same microscopic
ice crystals begin to form in the koi's gill tissues. Gill cells
begin to rupture one by one, slowly suffocating the fish. The fish
may never 'freeze solid' in the conventional sense, but the fish
IS freezing to death on a cellular level. Ruptured
cells may heal over but are replaced with scar tissue that either
does not transfer oxygen or transfers oxygen poorly. The fish may
survive the winter but in a poorly oxygenated pond the fish may
show stress in the heat of July and August when dissolved oxygen
in the water is at its lowest. The pond owner may think the over-wintering
process was successful only to find fish going belly up in mid-summer.
Large koi seem to be harmed by superchilled water more so than small
koi. One explanation is that young koi are still in
the midst of their growth stage at one and two years old. This is when they
are actively putting on body mass the fastest. They may also have
a stronger regenerative ability at this stage and can thus regenerate
gill cells more reliably than mature fish. Another explanation may
be that small koi have smaller gill tissues which can access
smaller air bubbles in the water and therefore they have a higher concentration
of oxygen in their gill cells which in turn helps to deter the
formation of ice crystals within the tissues. More dissolved oxygen = less ice crystal
formation = less damage. This is all speculation on my part, but
the end result is the same. Big koi die easier than small koi in a
poorly wintered pond.
PROTECT THE WARM DENSE LAYER
OF WATER IN THE BOTTOM OF THE POND!
5) Keep Surface from Freezing Solid:
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.
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 you 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 open the 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.
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.
Good luck and stay warm!
Perry
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