Is soft water better for koi?

koi carpSome koi keepers have alleged that soft water is better when keeping koi. They believe that very soft water encourages enhanced growth and improved colour development. But they are wrong! Freshwater fish, including koi, should be kept in stable conditions and in water with a PH between 6 and 9. The degree of hardness should be no lower than DH6.

The degree of hardness is made up of two factors – KH and GH. KH is a measure of temporary or carbonate hardness and GH a measure of the total dissolved minerals in the water. GH is hard to change whereas KH can be altered relatively easily, both intentionally and accidently.
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Even fish can get sunburnt!

Koi by Hellsgeriatric (via Flickr)
Koi by Hellsgeriatric (via Flickr)

You might be surprised to hear that fish, including koi, can suffer from sunburn.

How could this be?

Water does provide a barrier to UV rays but middle and long UV wavelengths can penetrate water for a few centimetres, especially if the water is very clear. Which it would be in a koi pond! Koi wouldn’t normally choose to spend too much time near the surface of the water but may be forced to if the water is too shallow or they are struggling to get enough oxygen from it.

Coldblooded creatures

Koi are coldblooded creatures which means that their metabolisms speed up as the water temperature increases. They then require more oxygen but the oxygen available will be decreasing as the water gets warmer. The struggling fish move to the surface and become vulnerable to the UV rays. Fish may also move closer to the surface of the water if the pond is overcrowded.

Symptoms of sunburn in Koi

Fish may develop skin sores in the areas exposed directly to the sun including the top of the head, dorsal fin and upper back. The affected skin will first turn whitish in colour and then eventually becomes patchy, thickened and creamy. Fins will become frayed and as the sores develop, the skin flakes off leaving a whitish or pink coloured ulcer.

In extreme cases, sunburn can result in serious imbalances in the blood and then kidney damage. Bacterial and fungal infections may develop and these might mask the original lesion, concealing the root cause of the problem. If you spot lesions in hot weather, always consider the possibility of sunburn. These secondary infections can be more serious than the original sunburn. Most fish will survive a case of sunburn if cared for properly but will often be permanently scarred as a result of their ordeal.


Certain chemicals can impact photosensitization in fish which means that the effects of the sun will be increased. If anything is to be added to the pond water, it is worth checking the photosynthesising properties of the substance before using it.

How to protect Koi from sunburn

It is important to ensure that your pond isn’t overcrowded as this will cause an excessive demand for oxygen. If you’re your pond is shallow, deepen it if possible. Avoid contaminating the water with photosensitizing agents and top up the pond with cooler water if it is overheating or evaporating too quickly.

You should check that your pump is working correctly and provide shade over the pond to protect it from direct sunlight. Better still, fit a koi shelter in the pond or construct a cave to provide a refuge for the fish.

If your koi have become lethargic in hot weather or appear generally unwell, they may be suffering from sunburn. In addition to the aforementioned preventative measures, consider the use of a fish stress reducer to help restore your stock to good health.

Can you grow plants in your koi pond?

koi carpThe short answer to that question is only if your fish will let you! Large koi may demolish or eat your plants but adding plant life to your pond is beneficial for Koi. The plants will also lift the look of your pond and transform it into a more beautiful feature of your garden.
But you need to choose the right plants and place them correctly so that they are not quickly consumed by the fish.

The benefits of aquatic plants in a koi pond

Aquatic plants are considered to be good additions to any koi pond. They help to increase oxygen production in the water and they keep the water cooler in hotter temperatures whilst creating shade for the fish. In spring, submerged vegetation provides a surface on which female koi can attach their fertilised eggs.

Plants also prevent the spread of algae as the shade they provide limits photosynthesis. Plants create a natural filtration system which restricts the formation of blanket weeds.

How to introduce your plants

The best way to introduce plants into your pond is to build a plant shelf. This can be constructed
along the edge of the pond. You should weigh down the plants with large rocks or stones as this will form a barrier between the plants and the fish and so restrict the number which are eaten! Do be aware that the plant shelf might make it easier for predators to feed on the fish and so preventative measures may be required to protect your stock

Floating plants, shallow-water marsh plants and submerged plants can also be placed directly into the pond.

Floating plants

Floating plants feature vegetation which sits on the surface while the roots hang down in the water. With some species, the roots may attach to the bottom of the pond. These plants provide shade for the fish and are generally easy to care for. Consider featuring water hyacinth, water lettuce, water lilies or lotus. Keep an eye on the growth of these species as they can get a little out of control.

Shallow Water Marsh Plant

These aquatic plants are typically planted on the edge of your pond in the shallow water. Consider water iris and horsetail for your pond. Umbrella is also an option but will not survive a harsh winter.

Submerged Plants

These species are grown in pots and then placed at the bottom of the pond. They are great oxygenators and remove excess nutrients from the pond environment but may be uprooted and eaten by the fish. Fanwort, American waterweed and water Purslane are good choices.

You might have to experiment to see what really works in your pond. With a little planning, you should be able to plant your pond so as to improve the water quality for the fish while also creating a more attractive look. You never know, you could discover a passion for gardening as well as for koi!

A new kind of car pool

A little research will reveal all the advice you need to create a koi pond for your home. As we have explained on this blog, size matters and it is important to ensure that you can maintain good water quality.

Most people choose to build their koi pond using bricks or cement but one enthusiast has taken the unusual step of using a car!

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Japanese koi accidentally dumped on campus lawn

Japanese koi are associated with good luck and prosperity. But there wasn’t a great deal of good fortune about when a consignment of koi was delivered to a Chinese University recently.

Linyi University in Shandong province had been offered a donation of 13,000 live fish by a fishery firm. The consignment of fish was duly sent to the university and included some 3,000 koi. Unfortunately, disaster struck when the delivery was made. Continue reading “Japanese koi accidentally dumped on campus lawn”

Feeding koi by hand

Interacting with the koi in your pond on a more personal level is not only a source of great fun, but it can also be a very rewarding experience. Koi (like humans!) are known to have changes in mood and this is all related to how comfortable and safe they feel in their environment. One way to ensure that they remain happy is by Continue reading “Feeding koi by hand”

Caring for Koi in Spring

With the bizarre weather which increasingly seems to afflict the UK, it can be hard to know when spring has sprung! Just when you think that the winter is behind you, another wave of snow blankets the landscape in white and temperatures plunge. But eventually spring will arrive and your koi will begin feeding again.

The Stresses of Spring

With water temperatures going up and down like the proverbial yoyo, your koi may be feeling a little stressed! When water temperatures reach 40°F – 50°F your fish’s immune system Continue reading “Caring for Koi in Spring”

How to acclimatise koi to a new environment

It is crucial to acclimatise a koi to the water if you are returning or introducing it to your pond. You may have purchased a new fish, removed a fish temporarily for treatment, taken a fish to a show or built a new pond. In all cases, your koi should be acclimatised to the water. Continue reading “How to acclimatise koi to a new environment”

Japanese Koi Competitions

Koi are big business in Japan and 90 percent of the fish produced are exported. Hand-reared for their aesthetic qualities, koi have become a symbol of the country and a single prize specimen can sell for thousands of pounds. The fish recently hit the headlines worldwide when Donald Trump was snapped dumping a box of food into a Tokyo pond. Continue reading “Japanese Koi Competitions”