Overwintering Koi & Fish Ponds in UK


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Page Summary:  One of the advantages pond keepers in South Africa have is that they dont experience long hard cold snaps so freezing ponds are rarely a problem and if it does ever happen it means a thin film of ice lasting maybe as long as until 10am the next day. Unlike for UK Koi keepers its rare for a suitably built koi pond in South Africa to experience prolonged low temperatures of about 8 degrees. This means in South Africa koi pond keepers do not have to resort to ice prevention measures. But this site is about koi and gold fish ponds for winter conditions in the UK not my country South Africa.

Feeding Koi in Winter...

Koi (Carp) are built to withstand very cold water and that means water which is actually frozen over for long periods of time in extreme winter weather. However its important to maintain vigilance and carry out some basic winter pond care.

Probably the most important thing to be done to ensure your koi or goldfish get through the winter in good condition is to make sure that you pond is cleared of debris long before winter arrives and generally put into good condition.

That means cleaning your pond (and biofilter) in Autumn.

The last thing needed to maintain health in a closed koi pond system is a high population of intrinsically harmful bacteria living in dormancy in the 2 inches of settled debris at the bottom of the koipond.

Sponsored Products...

Koi Food BradshawsEvery koi keeper buys food. All koi foods are not the same. Bradshaws Koi Food (and Wheatgerm) is as good as the best for quality and fantastic value for money in great sensible koi food packaging.

Hozelock Pond Vacuum Keep that pond bottom clean with reliable Pond Vacuum

Floating ice preventer

There are simple low cost pond water floating devices that allow a hole in the koi pond ice to be maintained to allow noxious gases to escape from pond water.

This is the Velda floating ice preventer ... click the link to see other types

Consider buying a suitable pond vacuum (see above) to keep the bottom of your pond clear of organic and inorganic debris which looks unsightly and is a breeding ground for anaerobic and pathogenic bacteria.

These potentially harmful bacteria have a habit of reaching infectious levels once warmer temperatures of pond water are experienced in Spring. It just so happens that this coincides with koi which have withstood a harsh winter not being in the ideal condition to ward off a potentially serious bacterial pond water attack.


Ideas for Winter Koi Pond Care

Feeding of koi in winter should be avoided. It is unnecessary and Im told that koi can live 150 days quite easily without artificial food. If youve fed your koi or goldfish well in summer and put them on a leaner diet of wheatgerm in autumn you will have done a good job or getting your koi fish ready for winter dormancy caused by severe drops in fish pond water temperature. Koi start to become lethargic at temperatures as low as 10 degrees C and at 8 degrees have probably stopped moving around very much at all. As temperatures fall lower for prolonged periods the koi will start to move less and less until eventually the koi (and to a lesser extent goldfish) sink to the bottom of the pond and enter a virtually motionless state. The koi have started to conserve energy for a prolonged period.

Koi Food BradshawsWheatgerm is a great koi food for use in the autumn months and also for occasional use in tiny quantities for those days in winter when the sun shines, conditions are breezy, the pond water warms and the fish start to move.

If youve cleaned out all the muck and debris out of the pond and biofilter created by the those windborne falling leaves, in their once splendid autumn colours, bird droppings, fish faeces, soil, dead beasts, and whatever else found its way into the pond  and youve given that biofilter a good clean out then youre well on your way to tackle winter koi keeping.

Hozelock Pond VacuumThe picture is of the hozelock pond vacuum model but there are a few different kinds you can choose from... from very cheap to the very expensive (OASE Pondvac models are the best by far but also the most expensive)

Its important to clean out the settled debris in the fishpond since it will be a source of pathogenic bacteria in the spring when weather starts to warm up and all of Gods creatures, good and bad, wake up as well.

Autumn is also a very good time to get those aquatic plants cut back and if you have sub tropical water lilies it's time to take them out of the koi pond and put them in a warmer place.

Here Comes Winter. How Come my Koi Don't Die in a Frozen Pond?

As I write this the UK has already had a week of relentless snow and cold weather. On one day something like 40% of the working population couldn't get to work (or didn't want to) because of the severe snow and wintery weather. Those gentle autumn frosts in September quickly became blizzard-like, sub zero and prolonged low temperature heavy-frost nights. Pond water started to freeze and stay frozen providing a thickening window through which to watch your koi lying motionless in water that now has a temperature of exactly 4 degrees C.

How do I know the water temperature is 4 degrees C and not closer to freezing? Well the answer is that water exhibits an important physical characteristic in that at 4 degrees C it reaches a maximum density and therefore sinks. Ice thus forms at the cold zero degree surface and as this low temperature is maintained the ice gets thicker but the rate of ice formation reduces dramatically because water below the ice surface is insulated by the ice layer. As the ice gets thicker it also starts to form more slowly until an equilibrium point is reached

It is in this 4 degrees layer that the koi, gold fish or other pond fish bide their time until more favourable conditions are experienced.

This remarkable and unique property of water allows the world to survive and not just koi or goldfish.

Koi dont mind cold winter weather. They are used to it. Koi and Gold Fish "hibernate" by remaining motionless on the bottom of the garden pond whose water is now exhibiting crystal clarity (no need for that UV pond clarifier this winter).

Your Kois metabolism has slowed to almost a stop, they dont need food and they use up hardly any energy in their motionless state. Your Koi and Goldfish have started to hibernate.

Under these frozen pond water conditions the metabolic processes of koi, gold fish and most aquatic life has slowed to an almost stop. The koi or gold fish and other fish use little energy through their motionless behaviour and the dramatic slowing in metabolism.

In any frozen pond it's important to release any build up of noxious gases by if at all possible by maintaining a small hole in the ice layer. BUT don't crash and bang the ice layer to achieve this.

To vent the pond of noxious gases that build up under the ice surface consider using a simple low cost floating device that keeps a hole open.

Floating ice preventerThere are simple low cost pond water floating devices that allow a hole in the koi pond water ice surface to be maintained to allow these noxious gases to escape from pond water. There are also low wattage (100 Watts) "pond heaters" that maintain a hole in the ice surface.

This is the Velda floating ice preventer ... click the link to see other types

In South Africa where we have many swimming pools suitable for swimming in summer but damn cold in winter heat is conserved by floating the equivalent of strong bubble-wrap on the pond surface. This technique can quite easily be adapted to conserve heat in a winter koi pond and the koi will probably benefit from this approach.

We also have the luxury of almost continuous sunshine in winter making all sorts of solar heating options available for serious pond keepers. Now winter solar in the UK... Im not too sure of that!

A golden rule... dont feed koi, or gold fish in winter. Just dont

Keep Your Koi in the Spare Room

I know it gets cold in that spare bedroom but its warmer than outside. If you do this make sure you use pond water and not tap water and do not feed the koi fish at all under any circumstances.

Where's All the Blanketweed and Algae Gone?

One of the things you may well notice about your koi pond and especially so if you had suspended algae in your fish pond during summer... like a miracle the pondwater becomes crystal clear and free of that nasty blanket weed experienced in summer. Why does the water in the fish pond clarify so much? The answer is that suspended algae causing green murky water or blanketweed algae like most other life forms in the pond also have metabolic systems that slow down in cold water and darker shorter days.

Viresco aqua and koi for algae and blanketweed treatmentThis appearance of clear winter pond water does not mean the koi pond algae problem is solved. Unless the problem of both algae and blanket weed is solved one or maybe both of these algae problems will return with a vengeance as the fish pond water warms up and sunlight hours extend next spring and summer. This would be a good time to add Viresco (available direct from the UK manufacturer)which will reduce the nitrate levels down to zero making algae formation (blanketweed or suspended algae) much less likely next summer.

Other articles about koi and fish pond care in winter

Pond Heaters. Heating koi ponds winter growth feeding benefits

Koi pond heating using gas electric in UK temperature control

Bringing fish and pond and water out of winter into spring

Koi goldfish pond covers over winter. How to look after pondfish

Over-wintering koi goldfish hibernation cold freezing water ice

Koi pond heating using gas electric in UK temperature control

Should I heat my new koi pond this winter. What temperature?

Temperature swings. Koi Goldfish Feeding & water temperature

To Feed or not to feed your pond fish or koi or goldfish

How Do I care For My Garden Fish Pond In Cold Winter

Frozen Koi Ponds & Fish Ponds. Ponds Freeze in Winter. Pond Care in Freezing Winter Weather

Interpet Koi Pond Test KitWhat the Does pH of Koi Pond Water Mean? Should I measure Pond pH