Pond water quality introduction

Water is so familiar that it’s easy to forget how remarkable it is. It has lots of unique properties that allow life to exist.

Water is most dense at 4°C, so fish and other aquatic life can seek out that denser 4°C water, which has ‘sunk’ to the bottom of ponds, and survive the winter even when it’s freezing in the upper layers.

Water is more temperature-stable than virtually any other liquid. It does not warm up or cool down quickly, so fish can enjoy stable conditions. Water can also dissolve almost anything, so fish can obtain all the minerals they need from the water.

Water is continually flowing thorough our environment. As water moves from the clouds to the sea – described as the ‘hydrological cycle’ – it picks up all sorts of things such as oxygen and any minerals it dissolves in rocks and soils. These give any water a unique profile or ‘quality’, so water from one river or lake, or indeed tap water, will be subtly different from that in another.

Water companies change  water slightly by adding chemicals to it. Some of these (chlorine and chloramines) are irritating to  fish and must be removed with chemicals or ‘water conditioners’ readily available from aquatic shops. Alternatively, there are many water-treatment units available that do a more thorough job, although they are more expensive, in the short term at least.

To avoid the hassle associated with treating tap water, some people use rainwater. This is not recommended for two reasons. Firstly, the rain might be polluted, particularly if you live in urban areas, because water picks up particles in the air it travels through. But, more importantly, because rain hasn’t passed through rocks, it is mineral-free, and these minerals are important for many reasons (see the Water hardness section).

 

Written by Adrian Love

 

Koi pond water temperature

Fish and garden ponds are naturally heated up by the sun. Ponds with large volumes of water and/or deep water will take longer to heat up. Furthermore, water requires a lot of energy to heat it up so it will take many days of hot sun before a pond’s temperature warms up. Conversely, the pond will keep its temperature for several weeks after the first cold snap of autumn. Koi, like all fish, cannot control their body temperature, so whatever the water temperature is will be the temperature of fish, too.

Koi are naturally warm-water fish and, in the UK, they are on the edge of their tolerable conditions. Unsurprisingly, they visibly respond to warm water and all their natural processes are geared to temperatures around 18–22°C (such as breeding, digestion and growth). Koi are much more active and responsive when it’s warm, leading many people to artificially heat their ponds.

High temperatures are not without their problems, though. Warm water holds less oxygen than cold water (see the Dissolved oxygen section), but because all the processes in a Koi are going faster when the fish is warm, its need for oxygen is greater. Therefore, in warm water, Koi can have oxygen shortages and might come to the top of the pond (where there is relatively more oxygen) to breathe. Also, in warm water some pollutants (see the Ammonia, nitrite and nitrate section) are more toxic and more likely to poison fish.

Cold water, of course, will contain more oxygen and some toxins are less harmful, but Koi will naturally slow down as it gets colder. Below 10°C, a Koi’s systems are on ‘tick over’. It will not digest particularly well so it feeds less. Its immune system, which protects a Koi against disease-causing organisms, is very limited in cold water so outbreaks can occur.

Heating a pond does keep fish more active for the whole of the year. It also means they grow all-year round. On the other hand, it is expensive and it is not an environmentally sound practice. If you do decide to heat your pond, make sure the fish have a cool period for a month or so in the winter because this lets a Koi’s body clock set itself to the natural seasons.

 

Written by Adrian Love
 

Dissolved oxygen in Koi ponds

Oxygen is essential for Koi to breath. Unfortunately, water only contains 3% of the oxygen that air does. And this small amount is also reduced by various factors:
• Water can hold more oxygen when it’s cold than when it’s warm. For example, water at 5°C can hold 40% more oxygen than water at 20°C.
• High air pressure forces oxygen into water. So when a low air pressure front comes over the country, the oxygen rises out of the water – like bubbles rising to the top of a lemonade bottle when you release the lid.
• Everything needs oxygen to breath, including the bacteria and fungi that decompose rotting material and waste. So when ponds are very mucky, the water tends to have very low oxygen levels – because the decomposers are using it all! Some disease treatments also strip oxygen out of the water.
• Plants (including the algae that causes green water) all use up more oxygen than they produce at night, so by dawn oxygen levels can plummet in ponds with lots of plants/algae.

Fortunately, Koi are rather more tolerant of low oxygen levels compared to many fish species. Nevertheless, their water should always contain over 5–6 milligrams per litre (mgl). Generally, the higher the value the better. In very unusual circumstances, there might be a dangerously high level of dissolved gases in the water (called ‘supersaturation’), which can cause damage to a Koi’s skin, but this is very rare.

Dissolved oxygen (DO) can be measured with a chemical test kit available from fish shops, although they can be quite tricky to use and read. Alternatively, oxygen meters are available that are very precise and accurate, but very expensive.

If you keep the right stocking levels (as recommended by your Koi retailer) and increase oxygen levels wherever possible, you are unlikely to have any problems with DO. Water picks up oxygen whenever it is in contact with it, so the more contact, the more oxygen is absorbed. Therefore, waterfalls fountains and venturis all increase DO.

 

Written by Adrian Love
 

pH levels in Koi ponds

The term pH is used to describe how acidic a substance is. Technically, it describes the number of hydrogen ions, which is what an acid is. Because the numbers involved are so long-winded, a scale was developed to quickly describe the concentration of hydrogen (H) in a substance.

In fact, the pH scale describes the amount that H is diluted and it runs from 0 to 14, with a dilution of 10 times for every unit of the scale (called a logarithmic scale). So, a pH value of 0 means that the H is not diluted at all and the substance is extremely acid. Whereas something with a pH of 14 means that the H has been diluted a huge amount (10, times 10, times 10, and so on, 14 times!). Such a substance cannot be called acid anymore so is described as alkaline or (more correctly) basic. The middle ground of the scale – where the substance is neither acid nor basic – is called neutral, with a pH of 7.

Most water is around neutral, although some areas of the UK might have slightly acid water (around 6), and many areas might have a pH of around 8. Koi are quite happy anywhere within this range, however, due to the relationship pH has with other water characteristics, it’s best to have the higher (more basic) conditions.

Too acid or alkaline conditions produce similar symptoms in  fish (called acidosis and alkalosis respectively) and include lots of slime (mucus), washed-out colours, laboured breathing and rubbing itself on the pond edges. Increasing pH levels is very easy – add limestone chips, mussel shells or oyster shells and so on (pop them in the filter). Reducing pH levels is much more difficult but there are commercial substances available.

Nevertheless, a very high or low pH means that something else is not right with your pond, so you must fix that first. Whatever you do, seek the advice of your Koi retailer and make any changes very gradually.

 

Written by Adrian Love
 

Ammonia, nitrite, nitrate in Koi ponds

Koi produce waste from the breakdown and ‘burning’ of foods to release energy. Most of this waste is in the form of ammonia, a substance that is incredibly toxic to fish. In nature, this ammonia would be diluted and washed away by huge volumes of water, but in ponds where we keep fish in relatively small volumes of water, the ammonia levels accumulate.

Fortunately, some types of bacteria break down ammonia to get energy – they add oxygen and form a substance called nitrate. Furthermore, a different sort of bacteria turn this nitrite into nitrate by adding more oxygen. Both bacterium live everywhere but can be given a home and ideal conditions in a filter.

Nitrate can be used by plants for food. Ultimately then, you start with food (fed to Koi) and finish with food (fed to plants), so there is recycling going on. This process is called the nitrogen cycle, since nitrogen is the element common to ammonia, nitrite and nitrate.

All waste is a potential source of ammonia, and the waste you can see (fish waste, uneaten food, and so on) is just the tip of the iceberg. Most of the ammonia released by Koi exits from the gills and you can’t see it.

All three substances (ammonia, nitrite and nitrate) can be measured with widely available test kits. Follow the manufacturer's guidelines because the toxicity of ammonia varies with the pH of the water (in acid water, ammonia is less toxic). In any case, generally you don’t want any ammonia at all (0.0mgl), nitrite should be less than 0.1mgl and nitrate should be less than 20mgl. With all three, always aim for zero. The odd brief peak in levels probably won’t kill fish immediately, but it’s vital to find out what’s causing the blip and sort it out.

High levels mean there’s too much waste and not enough filtration. Causes may be too much food, too many fish, too little water going through the filter, too small a filter, or that the filter’s blocked, dirty or isn’t working well (it could be too cold, too low in oxygen, or damaged by chemical treatments, for example).

In the long term, at least one of these areas needs to be looked at if you find levels of ammonia, nitrite and nitrate creeping up. In the short term, carry out a water change (10–20% every day) and maximise aeration in the pond because both these things will reduce a Koi’s stress.

 

Written by Adrian Love
 

Water hardness in Koi ponds

Hardness is one of the most misunderstood characteristics of water, because it involves some rather complicated chemistry. In a nutshell, hardness describes the levels of minerals in water, primarily minerals containing calcium (Ca) and to a lesser extent, magnesium (Mg).

Water with lots of these minerals is called ‘hard’, whereas mineral-poor water is called ‘soft’. Water hardness is important for two main reasons: firstly (and most importantly), it keeps pH levels stable and relatively high. In any pond, pH tends to get more acid over time – even over 24 hours, natural processes can cause pH levels to change.

By absorbing or releasing acid, depending on whether it’s plentiful or scarce, hardness minerals effectively keep pH constant, which is very important to the well-being of the fish. Because they prevent extreme shocks in pH, the hardness minerals are described as ‘buffers’, and the level of buffers in the water is called its ‘buffering capacity’. As the minerals are used up in the pond, the buffering capacity will decrease over time.

The second reason is that fish use minerals to make their structures, like scales and bone. Koi kept in water with high hardness levels will have brighter skin, scales and colours.

It’s easy to see why high levels of water hardness are so desirable, and this is easily achieved in ‘soft’ areas by adding limestone chips or shells (such as mussel or oyster shells), commonly in the filter compartment.

Hardness may be described in terms of degrees (°dH) of ‘general’ or ‘carbonate’ hardness – abbreviated as GH or KH – and these two types of hardness are simply a measure of different parts of the hardness minerals. Both are very easily measured with test kits. Anything over 8°dH for GH and 4°dH for KH is fine. High or low levels will probably not directly impact on a Koi’s health, but the appearance of the fish might be affected and the repercussions on other aspects of water quality should not be underestimated.

 

Written by Adrian Love
 

Summary of Koi pond water quality

Water characteristic	Unit of measurement	Koi's preferred level	How to test for it	How to increase levels	How to decrease levels
Temperature	˚C	10–30˚C	Thermometer or electric meter	Electric or gas pond heater	n/a
Dissolved oxygen	Milligrams per litre (mgl) or percentage saturation (% sat)	Above 5mgl or 75% saturation	Test kit or electronic meter	Waterfall, fountain, venturi, running water, lower stocking levels	n/a
pH	Units of  pH scale	7–8	Test kit or electronic meter	Limestone or shells	Unlikely, but pH buffers are available
Ammonia Nitrite Nitrate	Milligrams per litre (mgl)	0.0mgl  <0.1mgl <20mgl	Test kits (electronic meters are available)	n/a	Low stocking, appropriate feeding, efficient filtration
Hardness	°dH GH °dH KH	Over 8 Over 4	Test kit or electronic meter	Limestone or shells	Unlikely, but products are available