Winter and Your Pond
First: standard disclaimer. We live near Chicago,
in Zone 6. If you live in milder or colder zones, adjust accordingly.
Only the most fortunate of us Pond People have
the luxury of a year-round season. The rest of us have to put up
with Ma Nature at her most unpleasant, otherwise known as winter.
Our fish will shut down most of their nonessential systems, including
their gut and their immune systems, at water temperatures approaching
45 degrees Fahrenheit, and our bioconverters are shutting down as
well. At the same time, any trees and plants around the pond are
attempting to dump a ton of biomass in the form of dead leaves.
Our primary job in this
case is to begin early in the fall and prevent the eventual problems
this combination of events will produce.
This is by far the most important thing you will do to protect your
fish, especially if your plan is to leave them in the pond during
the winter. (This is necessary for all but the smallest of your
koi. Koi larger than a couple of inches will quickly overpower any
standard aquarium filtration system. Any fish brought in for the
winter will need an established large-capacity bioconverter and
plenty of water.)
While the air and water
are still warm, get into the pond and remove all of the season's
sludge and debris. This will minimize the generation of breakdown
gases (primarily hydrogen sulfide) during the months when your pumps
are shut down, your water is not moving, and areas of low oxygen
content can develop in deeper parts of your pond.
If you have goldfish,
you will be pleased to know that the comets, shibunkins, sarassas
and other long-bodied types are hardy in this area. Round-bodied
fancy golds like lionheads, ranchus, ryukins, are marginal. We take
ours in, as our marsh garden is somewhat exposed. Other folks leave
theirs out, but we can't recommend it; our winters have been too
Second: Leaf Netting.
Once clean, the pond should be protected with netting fine enough
to keep leaves out. The netting needs to be supported by a framework
high enough to keep it several feet above the water's surface (
to keep fish from becoming entangled) and strong enough to support
not only the net, but also the plastic sheeting you're going to
put over it as air temperatures drop below 40 degrees at night.
I've found that the best solution to this is a greenhouse or "poly-house"
kit, usually formed from pre-bent 1 ¼ inch galvanized pipe.
Kits of this type can be had cheaply from Midwest
Trading in St. Charles, IL.
Third: Know when to stop feeding.
Fish are cold-blooded. When the water temp drops, the fishes' digestion
stops. Food will ferment in the gut and kill them. In cool weather,
it may take three days to completely digest a meal, so you need
to be reasonably sure the water temperature will stay up for the
next 72 hours. They will still beg when it's sunny, but don't give
in. Fall and spring food should be low-protein - easier to digest
- Cheerios will do nicely.
Fourth: Ice Management.
You'll need to keep at least some of your water surface ice-free
during the coldest months to allow for gas exchange. Without protection
from wind, even the most robust trough heater will be overwhelmed
by a really cold Chicago-area winter, leaving you the unenviable
task of huddling out by the pond in subzero weather melting your
way through several inches of ice with pots of boiling water*. What
fun! An airstone set just below the surface of the water and running
"wide open" will help, but nothing beats protection from
the wind. Use 7-mil plastic over the pond. This gives a strong greenhouse
effect on sunny days, blocks the wind, and keeps the pond still
and quiet so the fish are calm.
There are a number of
high-tech solutions to frigid water, mostly in the form of pond
heaters of various designs. Electric heaters , especially trough
heaters meant for farm use, are energy hogs, usually not up to the
job, and rust out quickly, often creating short circuits in your
pond and injuring your fish**. More elaborate systems involving
heating coils filled with a heat-exchange fluid and heated by a
modified hot water heater (usually powered by natural gas) can be
expensive to install and run. The coils require a basin of circulating
water to keep water temperatures up or need to be put into the pond
itself. This may require considerable redesign of your pond at a
tough time of year.
A flashier and much more compact system
based on the instant water heaters becoming popular in newer homes
allows reverse exchange flow through a heat exchanger and can be
hooked directly into a pond's main return. It can also be run off
propane. More information can be obtained by contacting Keirin
In any case with water
heaters, your target temperature at the bottom of the pond is 39
- 42 degrees. The fish need the rest they have evolved to expect.
If you have a January thaw with bright sunny days, you may need
to turn the heater off. At 50 degrees, parasites and harmful bacteria
become active. Fish won't have an immune system until the water
hits 60 degrees. Also, if the fish wake up enough to move a lot,
they are burning their fat faster. This is not good if we continue
to have long, cold springs.
For those of us on the
"low-tech" (see "cheapskate" in your Funk &
Wagnall's) end of things, if you have set up your weather cover
and secured a layer of 7 mil poly-house covering over it, simply
shoving a $30 Home depot oil-filled radiator under the cover in
a secure and level area and adjusting the heat level to a setting
that keeps the air temperature just above freezing will do the job
just as well.
Continuing to run your
water system at winter temperatures will "supercool" the
water, disturb and eliminate the warmer water stratum at the bottom,
and overstress your fish, resulting in a very high mortality rate
come spring. The less you mess with the pond in the winter, the
better your fish will do .As the water temperature approaches 40
degrees, turn off your pumps and filters, and either drain them
or protect them from freezing. Frozen water expands significantly
and will explode your piping. Pull your airstones up off the bottom
and leave one or two running just below the water's surface.
As the water cools, water
at around 39 degrees will settle to the bottom of your pond. Your
fish will congregate there, since it'll be the warmest part of the
pond. Koi handle temperatures down to 39 degrees without undue stress,
and will stooge around near the bottom, nibbling a little algae
all winter and living off stored fat. The less they are disturbed,
the less fat they will burn and the better their condition will
be in the spring.
* Don't break the ice! Water is not compressible. The shockwave
can kill or injure fish.
** Electrical current through water causes permanently bent backbones
© 2005 Robert D. Passovoy, MD
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