Clear Water - How to Get It!

Submitted by Chris Neaves on Mon, 01/29/2018 - 15:48

I Can See Clearly Now

The words of the song - "I can see clearly now the rain has gone" could be re-written - "I can see clearly now the solids have gone". As stated in previous newsletters - biological filtration will produce pure water - mechanical filtration on a pond will result in clear water.

Check point: The easy part of filtration?

Crystal clear water can be deadly to Koi as the toxins we have to deal with in ponds cannot be seen. The process of biological filtration, is in reality, the easy part of pond keeping. When it comes to clear water in the pond we are faced with the fact that the higher our standards of clarity for our water the more efficient the mechanical part of the filter system has to be. The more efficient the mechanical filter is at removing solids, the more maintenance it will require.

In streams and rivers there is, relatively speaking, limitless water. The water clears as the solids are washed down stream (to pollute and silt up our dams!) In the pond or water feature we are recycling the same water with the addition of some fresh water from time to time. This limited volume of water has greater pollution problems and solid build-up than in natural waters.

Our basic design for the pond should provide for the solids to be trapped in a convenient place so that they can be removed easily from the system and the pond itself should not contribute much to the solid pollution. Keeping plants away from the Koi is one way of reducing solid pollution in the pond. Plants in pots in the pond are an open invitation to your koi to rummage for new soft juicy growth. Larger Koi will enjoy every moment pulling and tugging the plants out of the pots and spilling the soil onto the pond floor. Many pond builders place gravel or clay on the floor of the pond. Undergarvel filters are sometimes placed in the pond.

Clay and gravel on the floor of a pond is a disaster if we desire clear water. Koi are bottom feeders and will vigorously explore the gravel and clay bed for crustaceans and micro-organisms that will grow there. The sediment will be continuously churned up into the pond.

Consideration should be given to the solid pollution from trees that beautify the garden and pond. For example Jacaranda trees are magnificent but will pollute the pond severely. Their leaves are small and when they shed them there are masses of solid matter entering the pond which is difficult to remove. Interestingly, while on the subject of Jacaranda trees over koi ponds I have never seen a clear pond under a Jacaranda tree. The water discolours to a reddy brown hue. The longer the leaves are left in the water the worse the situation. Does anyone have an explanation for this?

I believe the word "convenient" should be emphasised constantly in the design phase of a pond. Our design concepts should revolve around ease of maintenance once the pond is completed.

Check point: The purpose of removing solids.

It is a proven fact that the biological part of the filter system should be left alone and undisturbed for as long as possible. This is to encourage the biomass of bacteria to colonise the filter material as quickly as possible and with as much bacteria as is possible. Therefore, the first reason for removing solids from the pond is to assist the biological side of pond filtration to be as efficient as possible. In my opinion an efficient biofilter is one where the ammonia in the pond water is processed to less toxic substances in one pass through the biofilter. Therefore, the biofilter is efficient in is design. Converting the toxins in the water in one pass through the biofilter is achieved when the filter bed "matures". Mature filter beds are obtained by supplying the bacterial colonies with continuous large amounts of oxygen and impurities to feed on and by leaving the biological filter bed undisturbed for as long as possible.

One way we can assist the biofilter is to remove the solids from the pond system. Further, in order to obtain clear water the various types of solids found in ponds should be removed from the system. In theory only clear water should flow into the biological filter (more appropriately called the biological purifier). Why?

Ideally the biological purifier should consist of colonies of bacteria that serve to convert toxic ammonia into nitrite (also toxic) and then to nitrate and finally nitrate to free nitrogen. This process is interfered with by showering these bacteria with organic solids e.g. fish droppings, dead leaves and uneaten food. These organic solids are broken down by different species of bacteria, which consume much oxygen in the process thus competing with nitrifying bacteria for oxygen in the biofilter. Furthermore, toxic chemicals, such as hydrogen sulphide (smells like bad eggs) and ammonia are released during decomposition. The resultant ammonia will also place an additional load on the nitrifying bacteria.

If the solid matter is not removed from the pond system and is allowed to decompose, the environment will deteriorate. This is due to accumulating toxins, consequent acidification of the water, and declining levels of oxygen. Acid water thins the protective mucus coating of the fish, and making matters worse, encourages disease-causing bacteria. Thus, if no remedial action is taken, the Koi will become stressed and susceptible to bacterial diseases.

Check point: Always input various ideas to your situation so that the filter is "right" for you.

There are arguments and counter arguments for specific designs of pond filters. The water should be pushed through the filter - the water should be sucked through the filter - the filter must have several chambers - the filter should have this - the filter should have that!

Discussing mechanical filtration may help with the broad concepts and principals we need to know to clear our water - the details can produce many healthy, fascinating discussions at the edge of the pond.

The substances that prevent us from seeing our Koi are known as solids. There are two types of solids that concern us - settled solids and suspended solids. Solids in the pond comprise a variety of different substances of varying sizes. We are all familiar with some of the common solids found in all ponds -  atmospheric borne dust, leaves, dead algae, algae trapped in various parts of the filter, dead bacteria, slit and fine sand washed into the pond. Some of these particles (the suspended solids) are so small that they pass through all but the most efficient mechanical filters and our water is never really clear. Ponds that are not cleared of these solids will eventually develop a black smelly sludge forming on the floor of the pond.

Air borne dust, a continual pollutant, contains various minute substances. These have to be removed from all surfaces in the house literally on a daily basis if the home environment is to stay healthy. In turn the rags and cloths, the vacuum cleaners and dusters that do the household cleaning have to be cleaned themselves. This is mechanical filtration and when applied to our ponds we must realise that mechanical filtration is the high maintenance part of koi keeping.

In order to attain clear water we should view our ponds literally as giant settlement tanks. They are simply calling out to the environment for solids to be deposited there. The pollution, the dust, leaves and anything else that settles on the surface of the pond is trapped by water tension, it cannot blow away or be wiped off as in the house. This is happening 24 hours a day, 7 days a week, 365 days a year. Levels of pollution vary at different times of the year. Most ponds are not at their best immediately after a rain storm for example. Dust pollution can be a real problem in South Africa during the dry months.

This pollution remains trapped in the water. The larger particles settle to the bottom or are swept away by a surface skimmer. These are easy to remove by flushing the bottom drains or discharge boxes or vacuuming out the pond. The finer particles remain in suspension and pass through most filters building up to the point where they cloud the water. Very fine particles never settle and remain in suspension. A test with a glass of cloudy pond water standing for a day or two will prove this point. Bacterial action will start on solids as nature starts the process of decomposition.

One of the debates on pond design - whether the pump should push the water or suck the water through the filter is not really relevant as both designs work equally well. However, logic dictates that all the pond water has to pass through the pump impeller at some time or the other whether it is being sucked or pushed. When our flow rates are anything approaching optimum then all the pond water will pass through the pump impeller every two hours or so. Filters that work on the principal of the water being sucked through filter chambers would have to have extremely high mechanical efficiency before the pump to prevent solids passing through the impeller at some time or the other. Levels of mechanical filtration of this magnitude would greatly restrict the flow rate to the point of the pump sucking dry.

Check point: Our friend the algae plant.

The solid saga in the pond is further complicated - the pond ecosystem produces solids every moment of the day. The most common solid that can really be a bug bear to all Koi keepers are certain types of algae. Before we march off and chlorinate our ponds to rid them of all algae we must show a little respect this essential water plant. There are thousands of varieties of algae. The furry type growing on the walls and floor of the pond is ESSENTIAL to the biological balance and strength of the pond.

Algae growing on the walls etc. is home to millions of micro-organisms - an ideal natural food source for your fish. The algae it's self is an excellent food source for the Koi. Spirulina, the wonder colour enhancer added to Koi food, is after all, only a variety of algae mainly from North Africa and Mexico. Never scrub the algae off the walls. If you are unfortunate enough to have a variety that grows particularly long and starts to affect the pump etc. remove the long strands but leave the last few centimetres against the walls.

Something that has been successfully done and may be worth considering - when constructing a new pond don't wait for the algae to grow. Visit a fellow Koi keeper who has an established pond that has algae growing on the walls of the pond, preferably a variety of algae that is short. Removing several pieces from the wall or water fall is easy. Place these pieces or strands under a stone on the waterfall or against a wall surface to seed the new pond with a variety of algae you want as opposed to leaving nature to her own devices. It is the same as planting the varieties of plants you want in your garden.

The algae that is really a nuisance for visual appreciation of Koi is the single cell suspended algae. This algae is not dangerous to Koi - they love green water, but we cannot see the fish. Looking through single cell algae blooms in the pond is similar to looking through smoke. The human eye cannot see the individual molecules of smoke, just the overall effect of millions of molecules. So to the human eye cannot see the individual cells of algae but we certainly can see the effect in the pond. Single cell algae can pass through many filters just as fine suspended pollution does. The algae that is trapped in the filter builds up rapidly causing blocking and channelling.

Single cell algae can reproduce it's self at over 30 times an hour. One day the pond can be clear the next - pea green. This single cell algae can be removed in several ways. It can be filtered out in an efficient mechanical filter. Another simple method is to install an UV light (ultra violet light). This lamp sterilises the passing algae preventing reproduction. The algae dies and the water clears. When the water clears, switch the lamp off and by-pass the unit if possible. There is the problem of removing the dead algae that manifests it's self as a fine powder, but this can be done in the mechanical filter.

Ponds in full sun almost always have a floating algae problem to some degree or the other. This is because of their very rapid reproduction rate stimulated by sunlight. Very bad cases are easy to identify - the owners never smile, the household phone bill is astronomical from all the frantic calls for help, the fish cannot be seen and the pond is a green soup.

Check point: Settled solids.

Settled solids are easy to remove - they are large enough settle out and more often than not large enough to be seen. They settle to the floor or walls of the pond or in a vortex chamber or in the discharge box or are trapped in gravel beds. Often settled solids are found on top of the biofilter where there is less turbulence. Opening the bottom drain or valve at the bottom of settlement chambers and discharge boxes is usually sufficient to remove settled solids. Ponds without drains must be vacuumed from time to time to remove settled solids.

Check point: Suspended solids.

Suspended solids are more difficult. These are the minute particles that interfere with the visual beauty of the fish - the water appears murky, perhaps has a smoky appearance, sometime we cannot quite pin point it but the water does not look "right". In the early stages of a single cell algae bloom the water takes on a discoloured look.

Suspended solids have a definite effect on the colours of fish. By this I mean the visual appreciation of colours. Any Koi dealer will know from experience that the clearer the water in his selling tanks the better the fish look. The next time you are choosing fish try a little experiment. Make a note of the lustre and colours of the fish in the pond with the clearest water. Then compare them to fish in a pond or holding tank where the water is not quite so clear. Don't compare size or price but merely skin lustre and colour brightness.

Why are the colours of the Koi so fantastic at our Koi show? Look a little beyond the fish - look at the water. The water has not been polluted with suspended solids. Another major factor is the fact the show ponds are cleaned each day before the public arrives. The bottoms are suctioned off and substantial water changes with mature water are affected. The settled solids on the floor are removed by vacuum and the suspended solids are removed with the water change. Food for thought.

From research literature it is clear that high loads of suspended solids may be lethal to fish and that sub lethal effects may result from continuous exposure to lower concentrations. In Southern Africa suspended silt concentrations are increasing in natural surface water due to various anthropogenic activities. (I haven't a clue what anthropogenic means but it looks impressive in the text!)

Suspended solids in natural water are both organic e.g. Phyto- and zoo plankton, other suspended organic matter and inorganic material (e.g. from soil). The suspended materials may be caused by the natural weathering of the rocks and soil, natural decomposition of plants, biotic matter, run off from the surrounding garden in the form of clay and sand/gravel. Some suspended solids may have toxic properties while others may be oxidised, which may reduce dissolved oxygen levels.

Check point: Koi are bottom feeders.

One of the reasons most Koi ponds are designed not to have gravel filter beds in the pond or clay on the floor of the ponds is that there will be constant solid matter agitated off the bottom by the koi which are bottom feeders. The results are that the water will never be clear to a high standard. There are other reasons why the biofilter should be outside the pond itself.

On the subject of clay being added to the pond floor or into a stream leading to the pond, we have to realise we are dealing with a closed system and the same water is re-circulated with a limited amount of fresh water being added. It is, therefore, very difficult to remove suspended clay slit from a closed system. It is very fine and remains in suspension for ever. In an open system the suspended solids are simply swept away down stream. Clay or gravel beds inside the pond do not produce the results we are striving for in our water features - clear water.

Although suspended particles may not have immediate effects on fish, in the long run scientific literature indicates that it may harm fish populations. Reduction in light penetration results in less photosynthesis. This in turn results in reduced plant biomass and food availability. Algae on the walls and floor of the pond, so necessary for the biological balance we want to achieve will have difficulty in growing. Clogging of gillrakes and gill filaments resulting in infection and possible death. Reduced growth rate and resistance to disease has been recorded. Very high levels of turbidity has effects on reproduction and egg survival.

We have established that the goals of mechanical filtration are to improve the clarity of our pond water with out resorting to chemicals that would be harmful to the fish. How do we achieve this?

Check point: The function of mechanical filtration.

The function of mechanical filtration is to separate the suspended and settled material from the water and collect it in a central location where they can be discarded from the system. Mechanical filtration is a visible form of filtering. You can see if the water is clear and free of detritus. Mechanical filtering is also, relatively speaking, the high maintenance area of the pond.

Most municipal waste water plants initially run water through a screen to trap and collect the relatively large particulate matter (which is termed sludge). This corresponds to the mechanical filtering of the larger solids in our ponds that can be accomplished with a chamber/box/container of some kind of light material such as shade netting on frames, shade netting in bags, filter pads, pleated cartridges, sponges, gravel beds, plastic rings, and if you are using the biofilter as a mechanical filter, the stone or plastic bed it's self. Another form of mechanical screening is a stream leading to the pond which is planted with water loving plants. As the water runs through the stream the solids are trapped in the root systems of the plants and are then decomposed by the bacteria present.

Waste water engineers and aquaculturists additionally reduce turbidity (particles suspended in the water) by using clarifiers, settlement tanks, vortexes, high rate sand filters and fine gravel beds that "polish" the water. There are an infinite number of designs that work. These will be discussed in detail in a future newsletter.

Check point: Out of sight, out of mind?

The settled solids and the suspended solids are thus trapped in a place where it is convenient to remove from the system. The hobbyist only eliminates this sludge when the mechanical filter media is changed or cleaned. Until that point, as the material collects in the filter, it is being broken down (mineralised) into ammonia and other substances by bacteria and very small organisms - all of which contribute to deteriorating water quality. When it comes to the detritus in a mechanical filter, an attitude of 'out of sight, out of mind' is just the thing the pond keeper must avoid!

We will discuss mechanical filter ideas and actual designs in detail, as well as looking at the pitfalls that can demoralise Koi keepers when it comes to clear water in another article.

Chris Neaves

Note: The Chris on Koi stories have been researched from scientific material and drawn from personal experience. Koi keepers needing further information or assistance can contact Chris Neaves at (011) 793-3478.


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