“Do I need to use a Koi pond heater in winter?” it’s a question that we get asked a lot, particularly at this time of the year, and it’s something that we looked at in detail in issue 20 of the magazine.
This short blog post features the start of that article. If you’d like to read the full article then check out our issue 20 magazine. It’s available in the back issues section of our online shop.
Do I need to use a Koi pond heater in winter? I could make this short as the simple answer is NO, you don’t need to heat! However, a lot of hobbyists are made to feel like bad Koi keepers or that they are keeping their Koi in inferior conditions if they chose not to heat. Koi are extremely versatile and can thrive in varied conditions in all parts of the planet. Given the relatively mild winters we have experienced in recent years there are a few simple techniques you can endorse to help you transition through winter without heating your pond.
Can Koi withstand cold temperatures and what are the associated risks?
Yes, overall Koi can withstand very cold temperatures. I think it would be fair to say that certain, individual Koi take a disliking to winter, you can look at these Koi as the canaries of the pond, and you may also find that such fish are always the first to show signs of ill health when a problem occurs in the pond. This is likely to be a simple example of an inherently weaker Koi, and as such, they are just more susceptible to health and/or environmental issues. As an example, younger Koi are far more susceptible than more mature Koi. As tosai, they are still in the developmental stage, and as a result stress episodes can have a far more profound impact on them.
There are a couple of breeders in Japan who have such volumes of Koi that they physically cannot keep them all inside over winter, they leave them in the mud ponds! These ponds are completely frozen over and remain like this for weeks, even months. The argument that Koi cannot withstand cold temperatures can be disproven but to have a balanced discussion we need to be aware of the potential pitfalls of cold temperatures and how we can respond to them.
Naturally, colder temperatures can heighten health issues because the Koi lack an immunity response when they arise, but this is where people cloud the issue slightly. Healthy Koi, in a healthy pond, can withstand lower temperatures than Koi that have depleted reserves from underfeeding throughout the year and stress through water quality issues, for example. The key to sailing through winter at lower temperatures is to prepare the Koi suitably and ensure they are equipped to get through lower temperatures.
When the temperatures drop, the activity of almost all biological functions slows down. This generally means that in the event of a health issue they can form slowly and in the case of parasites the Koi show little symptomatic signs as they are listless and lethargic in cold temperatures. If our Koi displayed this type of behaviour, it would ring alarm bells immediately and I would naturally investigate further. I guess my point here is not to become too complacent in winter and be aware issues can still arise, albeit, normally at a slower pace.
If you allow water temperatures to drop naturally then I would ensure that you don’t go into winter with niggling water quality issues. This is never ideal, but Koi will struggle even more to deal with stress factors, so it is important to not overlook this just because your Koi are inactive. In Japan, indoor space is premium, and you will often see heavily stocked ponds, this is where breeders use salt to block the impact of Nitrite. Salt can be a very useful tool at times, but its misuse can also open the door to other issues. If you decide to employ the use of salt, you must be clear in your objective and be aware that the salt will remain in the system until it is removed via water changes.
If you encounter a parasite issue when at low temperatures it can be difficult to overcome as many treatments on the market cannot be safely used below 8 degrees Celsius. You will also find that Koi tend to huddle together in cold temperatures, so it makes the migration of parasites from one Koi much easier in the event of an outbreak. Not being able to treat for parasites can be a scary thought but there are ways of managing the situation. An old-school remedy would be to salt bath your Koi, of course, this will not kill waterborne parasites, but it buys the Koi time.
Read more
To read all of this detailed article, order your copy of issue 20 today.
It’s available in the back issues section of our website.