Home - So you want to keep koi - A guide to water quality and more.

Too much detail ? Please go to 'So you want to keep koi. The Basics'.

 

OK, you are expecting an article all about koi! Well we could do that, but this article will predominantly discuss the environment in which to keep koi. We unashamedly take this approach because without truly understanding the conditions under which koi must be kept you will never keep healthy koi and you will miss out on all the enjoyment that the hobby has to offer. Yes, there is a little to learn and to think about, but taking this advice onboard will set you on the road towards trouble free enjoyable koi keeping. Keeping koi is not at all difficult just so long as you follow some basic rules. We have to introduce a little science, but as you read through you should begin to understand why this is important. So for now forget about building a pond, first you need to appreciate that koi produce waste products and toxins as part of their normal life process. You must understand how these waste products can be removed from the pond water and you must understand how to put systems in place to ensure that this happens. The particular toxins to which we refer contain nitrogen hence we need to discuss a process called the nitrogen cycle. Although not scientifically accurate, for the purpose of this article, different molecules containing nitrogen will also be called different forms of nitrogen.

A molecule, what is it? A substance composed of two or more atoms held together by chemical bonds. For example, a molecule of water comprises two hydrogen and one oxygen atom, a molecule of ammonia comprises one nitrogen and three hydrogens and a molecule of nitrite one nitrogen and two oxygen atoms.

An atom, what is it? An atom is the smallest unit of matter. Everything in the world is made of different combinations of atoms.

In a little more detail, nitrogen is never lost in the world it is just converted from one form into another. Some forms (molecules containing nitrogen) are very toxic to certain organisms, in other cases these examples are not only not toxic to the organism but are considered as the main 'food source'. It all depends on what sort of organism you are. Nitrogen is continuously moved around as a consequence of the action of living organisms, be it tiny bacteria or a human being. Many important molecules in the world contain nitrogen, some of the most familiar are proteins which comprise a major part of the diet of a huge range of different organisms. Nitrogen is needed for life and life continuously turns nitrogen from one form into another (from being part of one molecule to being part of another), this is why we talk about the nitrogen cycle. This article will discuss the importance of a particular form of nitrogen called ammonia and also about other nitrogen forms which are produced from ammonia. Some of these forms of nitrogen (ammonia and nitrite) are very toxic to fish so the article discusses how these toxins need to be converted into safer examples. Remember, living organisms of all types are continuously converting nitrogen from one form into another. What we need to understand is how to exploit the living organisms which as a consequence of their own life, like to convert forms of nitrogen which are toxic to fish into forms which are safe for our fish. This fundamental need drives our discussion about koi pond filtration and why it is an essential feature, both for the life of our koi and for the life of the organisms that we exploit to produce a safe environment for our koi.

 

The Nitrogen cycle

 

The nitrification stage of the nitrogen cycle

The nitrogen cycle or least sections of it (nitrification) is probably the most important aspect of koi keeping. Without it the keeping of koi would be almost impossible. Anyone overlooking this fact will never successfully keep the koi carp. Please be warned.

In very brief terms the nitrogen cycle represents one of the most important cycles found in ecosystems (aquatic or terrestrial). Nitrogen is used by all living organisms to produce a number of complex organic molecules that are essential for life. At any one time, most nitrogen in the world is in the form of nitrogen gas and the earth's atmosphere contains 79% nitrogen gas. Unfortunately although abundant, this form of nitrogen is not easily used by living creatures. It needs to be converted (carried out particularly by bacteria) into ammonia or nitrate, forms which can be used for incorporation into new life via further incorporation into, for example, proteins. Certain specialist bacteria are able to take nitrogen gas from the air and convert it by nitrogen fixation to the first potentially usable stage, ammonia. Other bacteria 'the nitrifiers' Nitrosomonas and Nitrobacter, together convert ammonia to nitrate. Much nitrogen is also generated and put back into the cycle by the degradation of organic matter including dead creatures and vegetation, again making it available for the production of more life.

So the nitrogen cycle involves the conversion of nitrogen from one form to another as a consequence of its use either as a source of energy or as a growth nutrient for generation or maintenance of life. Koi keepers only really need to focus on one part of the nitrogen cycle, a process known as nitrification (highlighted with red boxes in the diagram to the left). Nitrification is the conversion of toxic ammonia to much less toxic nitrate and is carried out by two crucial bacterial groups Nitrosomonas and Nitrobacter. Nitrosomonas converts ammonia to nitrite and Nitrobacter converts nitrite to nitrate. Both processes are oxidative, this means they cannot happen without oxygen and both are essential for the survival and health of koi.

 

Production of toxic ammonia - Where does it come from in the pond?

 

Essential actions for koi health Test the pond water to ensure it is free from the toxins ammonia and nitrite. Test kits are available from aquatic dealers.

Well, as shown above, most toxic ammonia is produced by the fish themselves as a simple consequence of them digesting their food. A large part of energy consumption in fish is covered by the breakdown of proteins supplied in the fish's diet. As we have mentioned proteins contain nitrogen. Fish do need some of the nitrogen present in their food but not as much as is present in proteins, hence they have to excrete it from the body. In carp metabolism 92% of unused nitrogen consumed by the fish is excreted as ammonia, the other 8% as urea. This is part of the continuous cycling of nitrogen by living creatures. Of the ammonia, 88% is excreted from the gills, some also from the kidneys. The main site for generation of ammonia from consumed proteins, is the liver (60%) other sites include the kidney, muscle and gut.

Ammonia is highly toxic to fish and fish constantly produce ammonia from the proteins in their food, so it is clear to see that in a contained environment such as a pond, something has got to be done about ensuring that ammonia is efficiently removed from the water. Ammonia is so toxic to fish that half hearted or inefficient methods of ammonia removal will not suffice. Even very low concentrations of ammonia will eventually lead to fish showing signs of ill health and susceptibility to disease.

In a pond, the first step in the conversion of ammonia to less toxic products is the formation of nitrite, this step is conveniently carried out by the bacterium Nitrosomonas as a part of its own life process. However, measurable concentrations of nitrite in pond water should be viewed no less seriously than ammonia. It is a fish toxin and its presence in any concentration cannot be ignored. Low nitrite levels will not suffice. If you are thinking about setting up a new pond or indeed if you have a pond and you are experiencing fish health problems you will never keep healthy koi in an environment where you can detect either ammonia or nitrite. Of course in the case of poor health there may be other issues to consider but you must check the water for these toxins. Most aquatic dealers will stock test kits suitable for detection of these toxins and will be able to advise you regarding their use.

Before discussing how nitrite is converted to a safe form of nitrogen (nitrate) we need to mention a point discussed in the associated article An Introduction to the Microbial World. The pond ecosystem is a community made up of many members doing different jobs. Fish do not completely digest their food; no metabolic process is that efficient. A lot of fish waste contains proteins and other materials that haven't been broken down by the fish's digestive system. Many types of bacteria are happy to carry on the job in the water environment breaking down the proteins for their own purposes so releasing nutrients for other life forms and also of course, more ammonia.

So now to the safer form of nitrogen. The final product in the nitrification process is nitrate, produced from nitrite by the bacterium Nitrobacter. This molecule is much less toxic to fish and levels of several tens of ppm (mg per litre) can be tolerated without ill effect. Note however, that nitrate is not completely without toxicity and measures should be taken to keep its concentration as low as possible. This can be achieved by regular changing of the pond water (approx.10% per week) and by the use of plants in the pond which will take up nitrate and other fish by products (phosphate) as part of their own growth requirements.

So where does this take us? Clearly it takes us to pond filtration. The building of the koi pond itself is a separate issue and one that has many features and details to consider but it will be discussed elsewhere. Filtration is an issue separate from construction but, depending on the kind of pond that you may construct, the two may also be intrinsically related. Only the simplest of koi ponds do not require detailed consideration of how filtration fits into the construction at the onset of planning.

 

Filtration of koi ponds an essential feature for life

What do we mean then when we talk about filtration of a koi pond? In its broadest sense filtration refers to the removal of relatively large particles suspended in the water, or removal of tiny particles (molecules, for example, ammonia and nitrite) dissolved in the water, by various means. So in more detail, although of least importance to the fish, first we need to think about clarifying the water. This involves the removal of the suspended particles from the water and is done predominantly for our benefit (clear viewing). Having said that removing as much solid as possible prior to or during the water's trip through the filter is highly desirable. Clear water means that the koi can be seen and enjoyed. Beautiful koi in cloudy water seems to defeat the point of keeping these fish. The process of removing suspended particles from the water is known as mechanical filtration.

Of much greater importance to the fish is biological filtration, the process of exploiting beneficial bacteria (Nitrosomonas, Nitrobacter and others) to eliminate waste products from water, many of which are either highly toxic or generally detrimental to fish. The bacteria required to carry out the desirable nitrification process (ammonia to nitrate) as well as those bacteria involved in other relevant nitrogen cycle reactions (conversion of nitrate to nitrogen gas) would be happy to live in any body of water supplying the right nutrients. This of course is demonstrated in rivers, streams and lakes, where bacteria of all types colonise the sediment at the bottom, the rock and gravel surfaces and all of the plant life as well as existing as free-living forms suspended in the water itself. As a consequence they do a great job of making the water safe for aquatic life. In a koi pond you have a somewhat different and unnatural situation. You have a relatively large number of fish in a small volume of water producing a lot of waste containing various undesirable molecules including the fish toxins. Typically 3,000 to 10,000 gallons (a common volume range for a koi pond) seems like a large volume, but the density of fish seen in even a moderately stocked koi pond far exceeds that found in nature. In addition, koi ponds often do not contain large rocky or gravel areas for adhesion and accumulation of bacteria and even if they did it isn't enough to cope with the vast quantity of toxic waste produced by the koi carp.

The amount of waste produced by koi is an important consideration. What might work for goldfish will not transfer to koi. The koi carp is a potentially big fish with an appetite to match ! Consequently it needs a high density of beneficial bacteria contained in a purpose built filter, whose sole job is to deal with all that waste. Purpose built filters contain what is known as a medium. Regardless of the type of medium chosen and there are many, the specific structure of each ensures that there is a huge surface area for bacteria to colonise. A common example is Japanese matting which as the name implies is a mesh of fine interwoven fibres creating a surface area the size of which would be difficult to calculate. You are effectively creating an artificial home for the bacteria. The importance of the suitability of the filter does not necessarily equate to expensive. Filtration systems suitable for application to koi ponds are available in many different shapes and technical forms and can cost between a few hundred to up to around £2,000 or more depending on the size of pond and fish density.

 

Three important parameters regarding biological filtration are oxygen concentration, pH and temperature. Conditions need to be acceptable for the bacteria to thrive. All of these parameters can be easily measured using commercially available test kits or equipment. Most aquatic dealersl sell them and can advise on their use. Oxygen levels must be maintained above 2mg/L in the filter. Because both nitrifying bacteria (Nitrosomonas and Nitrobacter) require large amounts of oxygen, the dissolved oxygen concentration entering the filter must be much higher than 2mg/L. For some filtration designs it is possible to add an air stone into the filter chamber itself such that a constant supply of oxygen can be maintained. Maintaining a high level of oxygen in the pond itself is also of course essential for the health of the fish. This can be achieved by further air pump driven air stones, a waterfall or preferably both. The method chosen is not important but failure to aerate efficiently will result in stressed fish and ultimately dead fish and poor toxin removal. The ideal pH for nitrifying bacteria is around pH 8. This value is also fine for koi (pH 7-8.5). With regard to temperature it should be noted that nitrifying bacteria cease to grow at temperatures below 12oC, hence, consideration must be given to the amount and type of food supplied to the fish at low temperature. The bacterial population will be slower in their ability to convert the toxins ammonia and nitrite to safer nitrate and they will be much less adaptable. The metabolism of the fish also requires a low temperature food, for example, one that is predominantly wheat germ protein based.

It would be impossible to try to cover all the different types of filtration units available in the industry. We will discuss some basic design principles only. The important element is to realise is that each design is set up to achieve the same thing. Every biological filter will provide a high surface area for bacterial adhesion, held in some kind of flow through unit where the bacteria are constantly in contact with pond water containing waste products.

 

Multi chamber filter systems.

These filters are a series of linked chambers containing either a medium to trap solids, or a medium that can support the growth of large amounts of beneficial nitrifying bacteria. We have discussed mechanical and biological filtration, we should also introduce settlement. It is far better to settle out solids from the water where they can be flushed to waste than to try to mechanically filter them from the water. Efficient settlement of solids prior to water entering a filter means that less of the solids are available to either settle in the filter itself, or to clog up the mechanical system (e.g. the brushes). Water containing a large number of suspended solids entering this type of filter is likely to lead to higher than ideal maintenance. So how do we achieve settlement? Settlement of solids can be achieved by the use of a vortex. It is simply a round chamber fitted either directly or indirectly ahead of the rest of the filtration system (one can be seen in the photograph above). As water enters the vortex it spins resulting in settlement of solids at the bottom of the vortex where they can be flushed to waste. It is always a good idea to put a vortex in front of any filter, as it will reduce the solids load entering a filter, improving clarity and filter efficiency.

Advantages - An effective system, so long as it is of adequate size for the pond volume and stocking density. Relatively cheap to buy or self-build.

Disadvantages - Fairly labour intensive, messy maintenance and takes up a lot of room relative to the pond volume.

 

Bead filter systems

Bead filters are interesting as the filter medium is designed to carry out both mechanical and biological filtration. The principle of the bead filter was developed from the commercial aquaculture industry. Many different designs now exist but they all follow the same basic principle. The filter is a sealed vessel which water can be pumped through from the bottom. Water flows through a packed floating layer of beads which trap solids in the gaps between the beads and which also act as a large surface area for bacteria to grow on. Cleaning the filter simply involves agitating the beads to release the trapped solids which settle to the bottom and can be flushed to waste. The beads simply resettle to the surface. Bead filters benefit from a pre filter or vortex.

Advantages - Effective, easy maintenance and a small size relative to the pond volume.

Disadvantages - Relatively expensive. Can't add air directly to the filter.

 

 

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