Living in a cold climate has some draw backs concerning Koi keeping. Ideally these lovely fish should be raised in a place where seasonal temperature's typically vary from 10°C to 30°C - while they may be cold blooded they are not cold water fish.
One of the most important factors to koi making it through our long winters is water temperature - below 7-8°C over too long a period and the koi are "surviving". Koi do not hibernate - they are not mammals. Koi are cold blooded or poikilothermic, meaning their body temperature/metabolism is regulated by their surroundings - WATER - as they have no mechanism in which to do so themselves. It's also important to note that their immune system is regulated this way as well - the cooler the water the lower the immune system, making koi vulnerable regarding health issues. Koi and goldfish can suffer from "hypothermia" so it is important to try the best you can to keep the ponds water temperature above 4-5°C.
Unless a pond is indoors here in Canada, those "ideal" temperatures just aren't possible all year round. Here in our part of Ontario summer air temperatures can reach well above 30°C with humidity while winter air temperatures can plummet far below -10°C. There are a few different ways to winterize an outdoor pond in which fish reside, dependent on the design, to insure things run smoothly in the following spring. Even with careful planning,.. sometimes there may be fish losses come spring. Our winters can be very cold and very long, sometimes to long...

Over the past years our methods for wintering koi have changed somewhat. Each winter presented it's own dilemma's which we had to adapt to in keeping our koi "alive". 2003/2004 none of our koi spent the winter outside.... we had moved and there was no pond. The koi were wintered in our heated garage in a wood/liner tank that Ian made. I'm not sure we will ever subject our fish friends again to Ontario's winter elements....

Below you find what "was" - meaning what we experienced and how we managed to get our koi through the cold months in past years.

For a couple years we over wintered a few koi in less than 1000gal pond. The pond was 3' deep. At first we tried using a small water pump(250gph) set about 6-8" deep to keep a hole open... this method was short lived. I woke one morning in late December to find the pond completely iced over. It took several pots of boiling water to thaw out a hole. That same day I purchased a "pond deicer", similar to a cattle trough heater(1500w !). We placed the deicer on a timer to come on for a few hours during the coldest parts of the day and night. This kept a large surface area free of ice and maintained the water temperature at around 5°C. The koi seemed ok, all huddled together at the bottom, occasionally on warmer days we observed them munching on algae.
Hoping so save some money on electricity we purchased a lower watt deicer in 2001. This worked well at keeping a small hole open but the water was much colder. We had tried covering the pond with a plastic shelter but found that the water temperature fluctuated far to much from day to night for our liking and seemed to cause added stress to the koi. In retrospect the volume and depth of the pond were contributing factors to our observations.
This was before the pond upgrade in 2002...

Dec 2002 the pond froze over so fast the ice was as clear as glass with a depth of 24inches.

Our Method:

Going into the fall we constantly monitor the pond water's temperature. When it starts sitting in the 16-18°C range we introduce a wheat germ based food, weaning of the higher protein diet, and cut back on the feeding schedule. Water changes of 10-20% are done weekly with filter maintenance At this time we transfer any 3-6" Koi indoors to over-winter in a DIY quarantine tank.

By the time there is a drop in water temperature to 13-10°C the Koi are on a strict Wheat gem diet and feeding is limited to once or twice daily in small amounts. We also observe them grazing more readily on algae. Once again we continue our filter maintenance and partial water change routine.

The 3500gph pump is replaced with a smaller 1500gph pump when 7-8°C water temp is reached, with the return placed 6-8" below the water's surface. The bottom drain diffuser is also shut down. The filter is given a good cleaning and a portion of the bio media is brought indoors, added to our indoor tanks filter.

When water temperatures are on a steady decline, surface water ranging 4-5°C , the 1500gph pump is removed. A final filter cleaning is done along with a small water change. A 100w deicer is then put in place. Now the waiting for spring thaw....

Dec 2001

Nov 2002

From our past experience in allowing the majority of the surface to ice over, the water temperature remained stable through out the winter season. Ice cover helped protect the waters surface from wind chill and lessened evaporation. We found that the average water temperature remained at 4°C during the course of the winter months. Depending on the depth of the pond, there may be a layering effect - surface being coldest, middle being average, and bottom sitting at the warmest. This can only happen if there is little or no circulation of the water. It is important to keep a hole in the surface for gas exchange.

Added Winter Cover...2002/03

We were noticing a decline in the ponds pH and KH... The 100w deicer has not been able to keep a large enough hole open so gas exchange had become an issue along with all the snow cover and the ice being so thick we believed the algae was dying off from lack of light - all this leading to the KH issue... So off to get some supplies and construct a temporary cover for the pond to see if it would help. The hope was that the cover would help retain some heat which should melt some of the ice to let more surface water open up to keep the water parameters more stable and possibly warm the water up a degree or two. The deicer was still in use and a small bubbler/air pump was added. One week later and there was a noticable improvement. The ice had started to retreat and become thinner, we did add baking soda(as a buffer) to up the KH. Outside temperature's had been dipping below 0°C but inside the structure seemed warmer and pond temperature held around the 4-5°C mark.

Plant pond was cleaned and pots dropped, no fish in here. This water garden at the deepest point is 24". Ice thickness in these pictures is roughly 12" and it's early December 2002. By January 2003 the pond was pretty much frozen solid. The gas bubbles sure make for an interesting argument that ponds with fish need an open hole for off gassing.

It is getting close to the end of active koi keeping season for many of us now. And preparations should begin in the next few weeks.
If you are in the east coast region of the USA from DC up to upstate New York ( this also holds true for England I’m sure) you will notice that your koi’s appetite is beginning to change.
Because your koi is truly part of its environment, changes are happening IN the koi and AROUND the koi at this very moment.
Your koi’s biological clock, triggered by night time water temperature, air surface temperatures and light changes, now is telling the koi what is about to happen- winter! This clock is also telling the females that spring breeding isn’t so far off and preparations must be made for that event as well. Therefore you koi will get hungrier! You will notice that they will eat more aggressively. Part of this is due to higher oxygen levels and better OPR readings this time of year which results in better water quality in general and part is the considerable influence of that biological clock.
You must now decide what you will be going with your fish come Dec. 1? Will they be under a protective tent or inside? Will they be left under ice to take their chances or will they be given only the illusion of winter ( mild heat and covered)? Only love, depth of concern, monetary value and economics will determine this answer.
In the ideal, your pond should already be netted ( berry netting available at any garden center or Home depot) to keep falling leaves, twigs and airborne materials from settling into the pond. The koi should be moved to a wheatgerm and fresh food diet about now and away from the high protein pellets. The number of meals and amounts can also begin to come down. I feed the same number of times this time of year ( three or four) but I reduce the amounts and already have opened my first bag of wheatgerm pellets. As water cools and the sumps are less burdened by organics, you will notice your koi’s white skin get much whiter.
Once Nov. Rolls around, your tent should be completely installed and ready to go as the cooler nights of late November will bring the water temps down considerably. During this time, you can usually depend on solar effects during the day and you can close the tenet at night to retain some heat. Remember, the tent acts as a heat space that separates your ponds water surface from the cooler air. My heaters usually start going on and off during the week of Thanksgiving. Once you water hits 50 F stop feeding. If you must, for emotional reasons, feed the koi- feed very small amounts and fresh food is better than pellets.
Now you are in the ‘ winter zone’. This can be real or man made. The difference being -a conscience decision to:
A) flirt with the carp population’s known survival ranges or
B) to limit the ‘ winter zone’ to individual koi’s optimal temperature range.
This is simply saying that at the most basic and primitive koi keeping level, temperatures near or below 0 C ( 32 F ) will test the survival abilities of each koi- young/old, well conditioned/ poorly conditioned. And nature tells us that a large percentage will make it through the challenge with only minor health issues the following spring. This older technique is pretty much passe in modern koi keeping but some water garden hybrid koi keeper types still practice it to this very day. And even this group is divided into those that let ice form and those that keep the ice off and keep things running. Both have their gamble. One allows gas to build and if a koi dies, that death can stress, sicken or kill the other fish. The no ice crowd will keep koi swimming in cold water and if the winter is long, the koi run out of gas and stress, sicken or die. This also allows winter precipitation to influence water parameters and water quality. And allows water to actually drop below freezing at some point- negating the passive warming effects of the earth. So IMHO the pond MUST be tented .
The second, more evolved approach B ( heat and tent) is to only allow temperatures to fall low enough to give the effects of the ‘ winter zone’ without testing survivability of each individual fish. This gives the desired effect in regards to the fish’s metabolic needs and seasonal shift but not an exhaustion or associated stress of a full blown winter survival challenge. This low end range then would be 45- 55 F/ 8-13 C.
The next decision that will separate ‘survival’ from ‘optimal’ will be the length of the ‘ winter zone’. The winters in the North East are long! As they are in England. In the primitive technique of koi keeping, a young koi may be asked to hang on for as long as 16 weeks. This is a lot to ask of the better breed koi from Japan. So parasites in spring, the illusion of a thing called aeromonas alley and general infection are all very real possibilities. The koi is simply weak and exhausted. An easy target for a pond that is becoming biologically active in an organically rich warming environment.
In the second technique, a man made artificial ‘ winter zone’, the winter cycle can be easily controlled. ‘winter’ can be as short as 6- 8 weeks and never dip below 45F. But be aware, low light conditions will still keep koi inactive and experiencing the seasonal influences.

* Regardless of which path you take, the pond should be kept clean and netted as the winter zone approaches. And normal maintenance should continue, albeit reduced somewhat. Water changes should continue, only smaller and less often. Sumps should be dumped, only less often.
* Equipment should also be checked as we all tend to not want to go out there! I also recommend a spare pump in reserve for that Sunday morning disaster!
* Drain all ‘ summer lines’ that can freeze. Make Thanksgiving weekend your drop dead date! If your are going to go ‘ primitive’ you need to consider freezing of lines- even if you keep the water running. This is why two speed pumps make some sense on one level and not much sense on another. Same is true with the use of ball values. Reduced flow with create a chance for ice to form and actually crack a schedule 80 ball value!
* stop all feeding once you reach your chosen ‘ winter zone’ . Another last minute meal is meaningless and can actually do more harm than good.
* the berry netting will keep ‘most’ leaves out but some how some will make it in so before adding the tent, make sure the bottom is clean.
* Look into buying a heater. This is the ultimate control over winter and the associated problems of the old way of keeping koi at the most primitive level.

I would like to thank JR for giving permission to post his thoughts here on Backyard Puddle. ~Terri

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