Is soft water better for keeping koi?

This is a topic we have looked at before and we are revisiting, as some koi enthusiasts advocate keeping their fish in very soft water. Should you do the same?

Is soft water better for keeping koi?
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How quickly should you turnover the water in your koi pond?

You may have read that it is advisable to turnover the entire volume of water in your pond every hour which might not be feasible in a larger pond. It is vital to turnover the water in your pond at a sufficient rate to remove ammonia and nitrite from the water. But what is that rate?

How quickly should you turnover the water in your koi pond?

Think before you increase waterflow

If you are fortunate enough to own a large koi pond, turning over the water every hour would require an impressive filter system and truly scary energy consumption! Before you plan to construct your own power station, it is important to consider that issues with nitrite and ammonia are less common in larger ponds.

The smaller the pond, the more likely it is to be overstocked and the harder it is to keep the water quality stable. Larger ponds can sustain slower turnover rates and you will probably find that a turnover rate of 2-4 hours is ideal unless your pond is enormous. You can test your water regularly using a proprietary kit but if you do discover ammonia in the water, merely speeding up the turnover rate may not help and might actually prove to be counterproductive.

Is your pond filter too small?

Poor water quality would most likely be the result of a using a filter of insufficient size. Speeding up the water flow will merely result in the pond water passing too quickly through the filter for it to process it properly.

Bear in mind that your pond’s surface, walls and floor will be colonised by the same bacteria that feature in your filter. The larger the pond, the larger the surface area, giving you a bigger bio-filter. Turning up the flow may achieve nothing more than a huge electricity bill!

In larger ponds, poor water quality will usually be the result of inadequate filtration or overstocking. Attend to these potential issues before considering adjusting the turnover rate of the pond.
It is possible to achieve outstanding water quality in a 30,000 gallon pond, for instance, with a turnover rate of 16 hours, providing the filter is up to the task.

Why does inadequate filtration time promote algae growth?

It is the breakdown of dissolved organic carbon compounds into simple inorganic compounds which is the most time-consuming aspect of filtration. The resulting compounds are ultimately incorporated back into living organisms.

This complex process is never instantaneous and will, even under ideal circumstances, take some time. It isn’t hard to see that if insufficient filtration time is available, intermediate products will be pumped out of the filter back into the pond. Which rather defeats the object of having a filtration system! Inadequate filtration often leads to excessive algal growth occurring because the filter is merely producing a generous supply of plant nutrients!

You have a delicate balance to strike if you are to achieve optimum water quality in your koi pond. It is possible to indulge in complicated calculations but ultimately, trial and error might be the only way to find the perfect combination of filtration, turnover and stock levels.

Koi keeping – 5 common mistakes

Koi are relatively straightforward creatures to care for but you can run into trouble if you don’t do your homework. Simple mistakes can lead to big issues! Here are the most common errors and how to avoid them.

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Why Koi benefit from natural sunlight

Most animals need natural light in order to thrive and koi certainly benefit from the sunshine. There are many ways in which sunlight will benefit your fish but it is important to strike a good balance of light and shade. There is much to think about when caring for your koi but their need for light should never be overlooked.

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Koi fish the subject of an RSPCA investigation

It isn’t often that you hear about an RSPCA investigation into the treatment of a koi! It’s usually the treatment of dogs, cats and horses which hit the headlines but a recent case involved a koi and there is something of a mystery surrounding the fate of the unfortunate fish.

Koi fish the subject of an RSPCA investigation
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Can you protect your koi pond from herons?

heronThere is nothing more soul-destroying than an heron visiting your koi pond. Your fish will start disappearing rapidly as these skilful and determined thieves work out how to bypass your protection measures to access one meal after another. You will soon understand that the term bird brain is a misnomer. Herons are clever – very clever!
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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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Koi stolen from Yorkshire pond

These days people will steal anything if they think there could be a few quid to be had and that includes your fish! To make matters worse, those targeting koi can be well-organised and efficient. Your fish can disappear without you sensing anything is wrong and that is exactly what happened to David Hobson.

Bedbound enthusiast loses entire collection

David Hobson is 74 years old and bedbound. He had built up an impressive collection of koi over 30 years and more. His family grew up with the fish and they were his pride and joy. David’s collection featured 35 koi worth between £25,000 and £30,000 but they have all been stolen.

Garden pond raided

The fish were taken from a pond in Mr Hobson’s back garden in Baildon, Yorkshire. Thieves took all of the koi specimens, leaving only a couple of goldfish and two mirror carp behind. The house wasn’t broken into and so the thieves had clearly targeted the fish and must have known they were there.

A great hobby for a man in pain

David had become a keen fish keeper as he suffers from arthritis. The pain caused by his condition prevented him from engaging in many activities but he could manage looking after the fish. Unfortunately, he recently suffered a stroke but his family have helped to keep the pond well-maintained and to care for the koi.

The koi boasted a mixture of colours and patterns and the collection was impressive. Following news of the theft, fellow enthusiasts posted expressions of sympathy on social media and some even offered David specimens from their own collections to replace the missing fish.

Protective net removed and replaced

David’s koi had been covered by a net which had been attached to the pond to prevent birds attacking the fish. The net had been unfastened, pulled back and replaced over the water during the theft, all without anyone in the house hearing a thing.

Will the fish survive?

Looking out of the window at the fish had been an enormous comfort to David who had become bedridden after the stroke. He had invested many hours in building the pond and 30 years nurturing the collection. He built everything from scratch, but all of his fish disappeared in just one night. He couldn’t believe that they had been stolen and is concerned that the trauma of being removed might kill them.

Pond security

If you have a koi pond, what can you do to prevent your fish from being stolen? In practice, it is very difficult to stop a determined thief. Obviously, locked gates are a must and it is best if your collection isn’t common knowledge. You should install floodlights with motion sensors as these may deter some intruders and if you can afford them, security cameras would be a good investment. Cameras may not deter all thieves but they might make it possible to identify them after the fact.

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.