COLD WATER CARE OF KOI
By Bryan Bateman
AKCA Koi Health Advisor
It is important to understand the effects of water temperature on
the ecology of a pond and the physiology of Koi. The purpose of
this article is to explain the changes that occur during the cold
winter months, and what we can do to minimize the negative effects
of these changes.
By now (late November/early December), the temperatures of non-heated
ponds in the Chicago area will most likely be in the mid-40s. Let's
first look at what has happened to this point.
When temperatures dropped below 60 degrees F, the Koi's immune system
had already begun to slow down (at 65 deg F, the immune system operates
at about 50% efficiency; at 60 degrees it has dropped to about 20%
Bacteria, both good and bad, are both still very active. The fish
still have healthy appetites, and the filter is operating at near
100% efficiency. Aeromonas bacteria is also quite happy at this
temperature, and this is why we are entering what has been called
At 50 degrees, the koi's immune system is operating
at only about 10% efficiency, while aeromonas is still at about
Some of the warm water parasites have begun to slow down, but the
cold-water parasites such as Costia and Chilodinella, are quite
content, and can pose a threat to our now low-immune protected koi.
Feeding should be almost nil at this point, although the filter
is still capable of converting ammonia to nitrites and nitrites
to nitrates, so these toxins should not be a problem.
The next magic number is 45 deg F.
This represents the low end of Aeromonas Alley because most bacteria
have slowed to less than 20% effectiveness. The koi, because they
are cold-water creatures (poikelotherms), have begun to enter a
state of torpor, and are most likely no longer interested in food.
They will be inactive most of the time, spending their days swimming
slowly at the bottom, where the water is warmest (more on this later).
At 40 degrees, which is very nearly the coldest
temperature a koi can survive in, the filter has ceased to function.
Bacteria, both pathogenic and beneficial, are at or near zero percent
effectiveness, as is the koi's immune system. In short, everything,
both ecologically and physiologically, has pretty much shut down.
Cold Water and Ammonia
It is important to understand the effect that
cold water has on ammonia.
As many of us already know, ammonia becomes less toxic at lower
pH levels. What many of us don't realize, however, is that it also
becomes less toxic at lower temperatures. Mother Nature is being
considerate here, because, as was explained above, our filters are
no longer capable of converting ammonia below about 45 degrees,
but our koi will continue to release ammonia thru their gills all
winter long, even though they are not eating. Ammonia levels could
become lethal under these conditions if this were not the case!
What about nitrites?
Nature is again on our side here. Below about 50 deg F, the
koi's metabolism has slowed, and along with it respiration, and
thus decreased opportunity to take up nitrites from the water. Once
the filter stops functioning, nitrites will no longer be produced,
but until that time, nitrites could still build to dangerous levels
if we continue to feed. Again, more good news. Nitrite uptake is
easily inhibited by adding salt at a level of only .1%, or about
1 pound per 100 gallons of water.
HOWEVER . . . (sheepish grin here) . . salt in
very cold water could mean trouble for our koi!
Fresh water reaches its maximum density at 39 deg F, so at this
temperature, it sinks to the bottom. This is why our koi will go
to the bottom during the winter, and also why we don't want to mix
our pond water during the winter. If we add salt to water, however,
the temperature at which it reaches its maximum density is lowered.
Salinity levels much over .1% will lower this maximum density to
the range of 35 deg F, which could be lethal to a koi. This fact
needs to be considered when adding salt to neutralize the effects
of nitrite (this is where water changes come in!!)
Cold Water Pathogens
Most parasites are warm-water creatures, and become
dormant or die off when the water drops into the low fifties. Notable
exceptions to this are Costia (or ichthyobodo) and Chilodinella.
These two parasites can be deadly at temperatures as low as 40 degrees.
The good news here is that these parasites are easily eliminated
with salt at .3% concentration (about 3 lbs per 100 gallons), or
if you are experienced in the use of Potassium Permanganate, a 2
ppm treatment will do the same. A salt or "PP" treatment
would be a good idea at about 60 degrees as the water is dropping
in the fall, to kill of these parasites. The same should be repeated
in the Spring as the water approaches 60 degrees.
Now about this Aeromonas Alley thing.
We know that it ranges from 60 degrees to 45 degrees F. We know
that the reason it exists is that our koi have a lowered immune
system while the aeromonas (as well as other bacterial pathogens)
are still active in this temperature range. The fact is, this is
the single most dangerous time for koi-health related problems.
A number of steps can be taken to reduce the risk
of bacterial infection.
- Since pathogenic bacteria thrive in high organic
environments, we should make every attempt to lower these organic
levels by keeping filters clean and minimizing the feeding of
our koi in these temperature ranges.
- A therapeutic potassium permanganate treatment
of 2 ppm, as mentioned above for parasite control, will also greatly
reduce the aeromonas population as well as reduce the organic
load through oxidation.
- Finally, there is a product on the market called
Lymnozyme, or Koizyme, which has revolutionized aeromonas control.
This product is an enzyme that out competes aeromonas for its
nutrient supply, and effectively reduces their numbers to manageable
levels when used according to directions. I strongly recommend
the use of this product in the Fall and again in the Spring.
Testing and Water Quality
Ponders will all too often ignore water testing
during the winter months. This is a big mistake! As stated above,
koi will continue to release ammonia even after feeding has stopped.
Once the filters have stopped functioning, nitrites will not be
a problem, but ammonia should be monitored regularly, and controlled
thru water changes as needed. In the Spring, it is a good idea to
check for nitrites, as the appearance of rising levels indicate
that the filter is starting up.
Another very important test is Carbonate Hardness,
or KH. Our ponds are still very much alive during the winter months
if the water is over 40 degrees F. This means that fish respiration,
nitrification, and photosynthesis are all producing CO2, which is
neutralized by the carbonates in the water. If the carbonates become
exhausted, the CO2, which forms carbonic acid in the water, will
cause a pH crash. Many fish deaths have been caused by this phenomena.
For short term control, baking soda can be used to raise pH and
replenish the carbonate levels. For long term control, oyster shells
or crushed coral can be placed somewhere in the pond where water
will flow past it, such as over an air stone or near a pump return.
A KH reading of 90 or above should be maintained for adequate buffering.
As a back-up test, pH should be checked frequently. If it shows
a trend downwards, this in an indication of insufficient carbonate.
Finally, and most importantly, WATER CHANGES.
This is the best way to control any and all contaminants in our
ponds. We will leave a garden hose on drizzle all through the winter,
thus avoiding a freeze up in the hose. This also eliminates the
need to add a dechlorinator, but if there is any question about
chlorine (some parts of the country use very high levels of chlorine
or chloramines in the water), sodium thiosulphate should be added
at about one tablespoon per 1000 gallons of water added.
With the information provided in this article, you will hopefully
have the knowledge to keep your koi healthy and happy throughout
the coming winter months. In the next issue, we will discuss bringing
our koi and ponds through the Spring warmup season.
(Authors note: much of the factual information in
this article is from a Koi Health Advisor Continuing Education course
written by Richard Carlson)
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