A koi fish pond needs to be really quite large, as koi grow pretty big – sometimes up to a metre long. If in doubt, build your koi pond bigger than you think you want it – the most common mistake new koi keepers make is to construct too small a pond, and expanding a pond after it's been built is very expensive, and a huge pain.
Koi pond volume
Knowing the volume of your koi pond is vital. You'll use it to work out the right amount any time you add anything to your pond (medicines, dechlorinator, etc), also to calculate what size pond filter and pump your pond needs. And most importantly, koi need a certain amount of space to be healthy.
As a rough guide to size, you need a minimum of 1 cubic metre of water for every three koi in the pond. Or, if you like to think in US gallons, about 100 gallons per fish. That's the absolute minimum koi need to be healthy. And bear in mind that yo may well want to add more fish – koi keeping can be addictive! And they breed… So it's really safest to build your koi pond at a larger size than you think you need.
Koi pond depth
- You should construct your koi pond at least a metre deep, and more is even better – 1.5-2m is perfect. There are several reasons for this:
- Shallow water is more affected by changes in temperature and weather, and changes of temperature make koi stressed and ill. Deeper water has a more stable temperature, which is better for your koi.
- Deeper water provides better exercise for your fish! If they don't get enough exercise, they can grow with big bellies, as opposed to the sleek shape that a healthy koi has.
- Deeper water also helps protect the koi from sunburn.
- And it makes it harder for predators to get to your koi, because they can hide in deep water.
And of course, the deeper it is, the more gallons you get for the surface area, so if your garden is small, going deeper can be a big help. However, bear in mind that koi will grow bigger in a pond with a larger surface area, than the same volume with a smaller surface area.
You might want to include an area of shallower water, though, where you can feed your fish, especially if you have children who will want to feed them.