A jumbo koi in your koi pond will attract the attention of all your visitors, even those that are not already confirmed koi lovers.

By Angela Beckx

The sheer size to which some koi grow is awe-inspiring, and the quest to grow and own the biggest koi in the world is the ultimate goal of some koi collectors. Koi can grow to over a metre in length, with the mono-coloured koi, rather than those that are tri-coloured, reaching the larger sizes. The relationship between pattern and size is due to genetic interaction that, more often than not, makes high-grade koi and jumbo size mutually exclusive characteristics. It is for this reason that the largest koi in a collection is most often a Chagoi, which is a tea-coloured koi, and usually the drabbest.

So, how can you ‘supersize’ the koi in your koi pond? Well, unfortunately, you cannot influence the genetic makeup of your koi, but you can maximise their growth by managing their diet and the environment you provide for them. It pays to bear in mind that with koi keeping bigger is always better, whether it is pond size, filtration size or even koi size. When in doubt always buy the biggest and best you can afford!


Feeding your koi top quality koi food that has a protein level of 40% or more, combined with a good mix of carbohydrates, fats, vitamins and minerals, will increase their size dramatically. In addition, from time-to-time, spoil them with treats like prawns, oranges, earthworms, fresh lettuce leaves and bloodworm. Many smaller meals throughout the day will be more effective than one large meal, all at once. Koi have small stomachs and thus prefer smaller amounts more often. You can use the ten minute rule to work out if you are feeding a reasonable quantity: if they have eaten all the food in the pond after ten minutes then you are feeding them correctly. If there is food left behind after ten minutes then remove it and the next time you feed reduce the quantity of food. Another method is to feed the equivalent of approximately 6% of the bodyweight of the koi, per day. Make sure you monitor how your koi are going as you do not want them growing too quickly and ending up with potbellies. Often the tamest koi in a collection with be the largest one because it is a food lover (even more so than the average koi) and so will always be the one that comes to say hello, in the hope of getting more food.


· Stocking levels

An overstocked pond has a negative effect on the growth rate of the koi in it. This is why it is so important to build the biggest koi pond possible, making it possible to keep all the varieties of koi you desire, without the pond becoming overcrowded. With fewer koi there is less competition during feeding times and, because they do not have to fight for food, their stress levels remain lower.

· Water temperature

Koi are cold blooded, but they are warm water fish. Studies have shown that pond water kept at 27C for around nine hours per day results in higher growth rates in the koi in that pond. For this reason summertime is the best time to feed your koi top quality food; they gain the most benefit from the food, using it all for growth, because of the optimum water temperature. Under these conditions a one-year-old koi can easily double its length in summertime.

· Water quality and air pumps

The best filtration systems give you excellent water chemistry, with low levels of organic wastes and dirt. This represents a stress free environment for the koi and lets them grow faster. Using air pumps also influences the growth rate in koi: tests show that koi convert their food into body tissue far more efficiently when dissolved oxygen in the pond is at its highest. High levels of dissolved oxygen enable the beneficial bacteria housed in the bio-filter to be at their most efficient in converting ammonia to nitrites and nitrates. Conversely, low oxygen levels result in suppression of the population of good bacteria which then allows ammonia and nitrite to increase to stressful or even potentially lethal concentrations in the koi pond. So, to avoid these problems and help your koi grow to enormous proportions I reiterate what I said earlier: make sure that the filtration system and air pumps you install are the biggest and best that you can afford.

Article written by Angela Beckx of Koi @ Jungle. Contact Angela on 031 2098781 or visit: Koi @ Jungle also stocks swimming pool products and equipment.

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