Whilst “filtration” on koi
ponds has become a somewhat controversial subject full of emotion, there are basic principles that apply to all variations
hobbyists may encounter. A wide variety of filters and bioconverters are available to the hobbyist. Koi Keepers must look
past advertising claims, past personal points of view and past complexity.
It is a fact that all filters and bioconverters
work. The human element transgresses certain natural laws of limitations and the failure of the system results.
“filters” and “bioconverters” will be used to describe the devices that remove solids and chemicals,
respectively, from pond water. More complete definitions will be given later.
A bioconverters is not working and will
not work in only two circumstances, 1) when it is new and 2) when it has been destroyed by chemical or medication treatments
to the pond or a complete lack of oxygen. In all other circumstances the bioconverters is working to some degree or the other.
Bioconversion is a simple, natural process in nature. Nature “works” – it’s as simple as that. The
number of living organisms that can be successfully accommodated in a limited volume of water (the pond) is determined by
the amount of oxygen removed from the water and the amount of toxic waste products added to the water during the process of
metabolism by all living organisms in the pond.
Our ponds are a limited volume of water. In order to successfully sustain,
in a healthy condition, a large number of koi, we have to recycle the same water. The recycled water is reconditioned by removing
the unwanted substances such as carbon dioxide, solids and nitrogen waste products then adding in vital oxygen. This purified
and rejuvenated water is returned to the pond as quickly as possible for the benefit of the fish and bioconverter.
is remarkable that all bioconverters and filters work. The filter system simply has to remove the fish excretion in the water
faster than it is added or it will build up to unacceptable levels. The filter must also remove organics such as algae faster
than they are produced in the pond or the water will go green. We simply have to add oxygen at a faster rate than it is removed.
The purified water must return to the pond as fast as possible.
THE SIMPLICITY OF IT ALL
The simplicity of filtration
on a koi pond is remarkable. The pond, the piping, the filtration, the bioconverter and the returning water to the pond can
be compared to the human body.
Our lungs introduce air into our systems and cells by making gaseous exchange possible.
The oxygen allows chemical processes to occur in the cells. This activates our bodies. The liver is a filter removing
toxins and impurities from our blood. The kidneys, colon and skin excrete harmful by- products to waste.
There is one
golden thread that enables all the functions to work – circulation of fluids within the body. These fluids carry a host
of vital substances from oxygen to white and red blood cells to hormones to carbon dioxide etc.
No matter how large and
strong the heart is (or a pump on a pond) it is useless, unless piping, in the form of veins and arteries, are free of restrictions
and open for the circulation of blood. The blood that carries nutrition and oxygen into the cells also carries waste products
away. Within the blood, a host of cells circulate to assist with the immune system, the nutrition and the oxygenation of the
It is an effective circulation that ensures the success of the organism.
A failure of any one of several
organs will result in the death of the organism.
For example, liver failure will result in the body being unable to filter
and remove impurities from the bloodstream. The body will then die. With kidney or bowel failure the same thing – impurities
in the body will reach toxic levels within a remarkably short time and the organism will die. A healthy circulation system
with strong heart, open veins, open arties, is the key to health within the body. The same principles apply to our ponds.
The human body is approximately 70 – 80% water. Our ponds are water. The fish are 80% water. The volume of water
of the pond is the living environment of our fish. The pond water is the piped (analogous to the blood vessels) to a pump
(the heart) and through various filters (equated to the liver, kidneys etc. of the body) for purification and rejuvenation.
The pond water is brought into contact with the atmosphere via waterfalls, streams, and /or venturis for gaseous exchange
to take place – exactly like the lungs. Oxygen is dissolved into the water and unwanted gasses pass out of the water
– just like the lungs.
Failure of any one of these systems will result in the death of the pond. When the pond dies
the fish die. The purpose of any filtration on a koi pond is to remove unwanted substances from the water – continuously
Just as removing the sugar and tea leaves from a cup of tea would need two different approaches, so too in
a koi pond different approaches for different problems are needed.
Impurities that are dissolved in the water need chemical
removal by bacteria (bioconversion) or with charcoal or zeolite. Impurities in the form of solids need mechanical removal.
A bioconverter is a remarkably simple concept. This involves providing enough space for naturally occurring bacteria to
grow on. These beneficial bacteria do a vital job in nature and in the pond of chemically changing toxic fish waste to less
toxic substances. It’s as easy as that.
Fascinatingly, the bioconverter is not only home to nitrifying bacteria
but home to countless other varieties, many of which have not been identified yet. This incredible diversity of microscopic
bacteria life plays a vital role in the success of our pond.
Piping that is clogged or piping that is too small or even
piping with numerous bends will restrict and reduce the flow rate, no matter how large the pump. These losses can be substantial
to the point of compromising the design of the system. Losses caused by restrictions in unhealthy veins and arteries in the
body compromise the circulation and health of the person. Exactly the same occurs in a pond.
STARTING AT THE BEGINNING
Viewing the entire pond system with the piping, the pumps, the various aspects of the filter and the returns it is literally
a circle. Where do we begin within the circle? After all, a circle has no starting point and no end. As water is the medium
in which fish live we will begin with the water.
Before the fish can be introduced into a pond, before bacteria growth
will occur, before there will be any life in the water it has to be activated. Nature activates water or the atmosphere for
that mater, with a gas – oxygen. We therefore, have to introduce oxygen into the system as the starting point. Once
oxygen is introduced into the water it must be circulated throughout every part of the system. Just as in the body, the oxygen
in the blood supply is circulated to every cell and organ. Should the oxygen supply be cut off from any part of the body for
long enough, that area will die.
In order to introduce oxygen into the bloodstream or into the pond water, the water must
flow – it must move. Once the water begins to move and there is a flow through the system, oxygen will be introduced
into the water with the natural gas exchange of the atmosphere and the system will become active and live.
The fish can
then be introduced into the system. Once the fish are introduced they will be fed. Once fed, impurities will be passed out
of the body back into the water. The combination of oxygen and excretion from the fish results in the growth of naturally
occurring nitrifying bacteria.
These bacteria will grow on all surfaces within the pond. There they begin their job of
converting the fish impurities to less toxic substances. Bacteria take time to reach large enough numbers to convert all the
ammonia to nitrite and at a later stage, to nitrate. It is as easy as that.
Ponds generate an enormous amount of pollution
or unwanted material.
This enters the pond system in various forms. Algae accounts for much of the organic build up in
a pond. Various other substances such as dust, debris, etc contribute to the build up of unwanted substances in the pond.
This organic matter ends up in the filter system and must be removed regularly to ensure a healthy environment. The maintenance
of a pond system is absolutely critical to the long – term health of the fish.
You would not consider trapping ten
dogs in a closed courtyard and never ever cleaning it.
The pollution these dogs would create in a short time would result
in illness, stress and death. Exactly the same applies to fish in the pond.
DOWN TO SPECIFICS
I would like to
examine some of the facts and explode some of the myths that have sprung up around filtration on kopi ponds. When we explode
some of the myths we are entering controversial territory. So let us clearly define what we are talking about and present
the facts. Enjoy this essay.
The solids that enter the pond water, even without any koi in the pond, can be dust, atmospheric
pollution, wash – off from surrounding soil and the biggest of them all – algae. Yes algae grows even without
koi in water! Look at your swimming pool if you do not add chemicals. Solids are removed by mechanical separation or mechanical
Definition: - Mechanical Filters will be referred to as filters. These are arrears where suspended and
settled solids are collected for removal from the pond system.
Myth: Ammonia is filtered from the pond water.
Ammonia cannot be filtered; it can only be chemically converted from one substance to less toxic substances by bacterial action.
Once we add koi to the pond and feed them they excrete (pass) ammonia via the gills and some faeces via the vent, Ammonia
is very toxic (depending on pH) to koi. This is removed from the pond water by bioconversion, not bio – filtration.
Let me explain.
Once there is ammonia present in the water and there is oxygen, a species of bacteria found in nature
– the nitrifying bacteria – start to grow immediately. These bacteria are chemolithotrophs. They do not filter
the ammonia out of the water they chemically convert ammonia to nitrite, in the presents of oxygen. Then after about 6 weeks
another species of nitrifying bacteria begin to grow that convert nitrite to nitrate. The nitrate can then be removed from
the pond system via water changes or small pockets of anaerobic bacteria that convert the nitrate to free or nitrous oxide.
Definition: - Nitrifying Bacteria, Bacterial species found in nature that oxidise ammonia to nitrite and then nitrate.
These are chemolithotroph species of bacteria that live in an oxygen rich environment, utilize mostly inorganic (without carbon)
compounds as their energy source, and require carbon dioxide (CO2) for their source of carbon.
In no part of this process
is the ammonia, nitrite or nitrate filtered – it is converted to less toxic substances. Hence the definition –
bioconversion. Bioconversion takes place mainly in the bioconverter. The (biofilter – in the older terminology) is the
place in the pond/filter system where we provide a media for the nitrifying bacteria to grow on. The nitrifying bacteria are
a species of bacteria that need a surface to adhere to. This surface – called a media – becomes coated with bacterial
colonies and a biofilm is formed.
Definition: - Bioconverter/ bioconversion – A bioconverter is a specialized
or dedicated area of the pond system designed to provide the proper environment for large colonies of beneficial bacteria
to grow. The nitrifying group of bacteria, the chemolithotrophs, as well as the organic consuming bacteria, the heterotrophs,
grows in the bio – converter. In some literature these areas are referred to as biological filters or biofilters.
the water in the pond becomes older various pollutants enter the water. Some via the wind and some are washed off from the
soil surrounding the pond. However, the single largest source of solid pollution in the pond is algae. A single cell algae
that can make our ponds go green over night can reproduce itself 30 times an hour in the sun. Algae grows all the time every
day of the year. There are thousands of species of algae. Some adhere to the walls and grow (produce) hair like growth. If
this growth is short all is well. If you have algae that grows particularly long and breaks off then it can get to the pump
and cause blockages. But algae does enter the filtration system all the time and is a major cause of sludge build up in all
parts of the filter system. Dead algae decomposes and this decomposition removes some oxygen from the system and adds ammonia.
Definitions: - Solids. Suspended solids are the non – dissolved pollutants that remain suspended in the pond
water. Examples of suspended solids are fine dust, pollen, dead algae and all fine solids and/or those solids near zero buoyancy.
Settled solids are the non – dissolved pollutants that settle towards the bottom of whatever reservoir they are
in. Examples of settled solids are heavier particles of dust, water logged organic material and leaves. One of the prime pollutants,
in terms of quantity, in pond water is dead algae. This accounts for as much as 60 – 70% of the organic material. However,
in some lightly loaded ponds, it may be 90% of the organic material that clogs up the filter system.
Let’s have a closer look at bioconversion first.
The nitrifying bacteria that do the conversion of ammonia etc.
are found naturally in nature. They need a source of oxygen. In other words they adhere to a media as well as all surfaces
and their food has to be brought to them.
Myth: The bacteria in the bioconverter will die if the pump is turned off.
Facts: This is false. The bacteria are very resilient. They will not die but become dormant. They are easily reactivated
when conditions improve
Myth: The bacteria will be damaged if tap water is used to flush the filters.
Not True. Once the bacterial colonies have established themselves they form a biofilm. Biofilms are very tough and protective.
Results of work conducted by Wirtanen and Mattila – Sandholm (1992b) and Mustapha and Liewen (1989) suggest that the
age of the biofilm affects the resistance of micro organisms to chemicals.
A significant fact discovered by all scientists
in the research papers on micro organisms I consulted with, indicate that mature biofilms were 150 – 3,000 times more
resistant to free chlorine at pH 7 and 2 – 100 times more resistant to monochloramine than were unattached cells and
new bacterial colonies.
Another interesting point – scientists have shown that much higher concentrations of antibiotics
are needed to kill bacteria in biofilms, compared to free – living bacteria. Originally, it was assumed that the biofilm
provided a physical barrier against the antibiotic; scientists thought that the antibiotic could not penetrate the biofilm.
This may play a role in providing protection.
However, there is evidence that the nature of the colonies themselves provide
protection. By growing in micro colonies, the outer cells protect the inner cells from the antibiotic that does penetrate
the biofilm, leaving the inner cells to grow and multiply. This is fascinating, so let’s have a closer look at bacterial
colonies – this is critical for our understanding of what is happening in our ponds let’s have a closer look at
Scientists have proposed several mechanisms for bacterial attachment to inert surfaces in aquatic
environments. Marshall et al. (1971) described microbial attachment to solid surfaces as a two – step process. In the
first, reversible stage, the bacterium is weakly held to the surface by electrostatic attraction and Van der Waals Forces.
During this stage, the attached cells may be easily removed. Keep this in mind when wondering about New Pond Syndrome.
scientist propose that the second stage of attachment is a virtually irreversible stage is time – dependent and involves
the physical attachment of the cell to the surface by complex polysaccharide material produced by the cell. This extra cellular
material has been described as a felt – like polysaccharide glycocalyx ( Costerton et al., 1981, 1978). As the bacterial
cells continue to multiply, micro colonies are formed, creating a biofilm composed of bacterial cells entrapped within this
In an extensive review of the role of bacterial attachment in the establishment of micro organisms, Notermans
et al., (1991) described three distinct steps. In the first stage, the bacteria attach to the surface. In the second stage,
the bacteria consolidate at the surface, often forming polymer bridges. In the third stage, bacteria colonize the surface,
growing and spreading over the surface.
The consolidation stage is critical to the continued attachment of the organism
to the surface. During this stage, the micro organisms produce extra cellular material that literally cements the cells to
the surface. At this point, the attached cells are not readily removed by rinsing (Schwach and Zottola, 1982).
association between the bacterium and its substrate persists long enough, other types of chemical and physical structures
may form which transform the reversible absorption to a permanent and essentially irreversible attachment.
The final stage
in the almost irreversible adhesion of a cell to and environmental surface is associated with the production of extra cellular
polymer substances or EPS. Most of the EPS of biofilms are polymers containing sugars such as glucose, galactose, mannose,
fructose, rhamnose, N-acetylglucosamine and others.
This layer of EPS and bacteria can now entrap particulate materials
such as clay, organic materials, dead cells and precipitated minerals adding to the bulk and diversity of the biofilm habitat.
This growing biofilm can now serve as the focus for the attachment and growth of other organisms increasing the biological
diversity of the community.
At one time, most scientists thought that biofilms consisted of bacteria randomly distributed
within a uniform slimy matrix.
However, once scientists began using new imaging tools like the Confocal Scanning Laser
Microscope, which allows viewing of hydrated living biofilms, they found that biofilm structures take a wide variety of forms
depending on their age and growing conditions.
Most of the bacteria in the world live in micro – ecosystems filled
with hundreds of different of other micro – organisms. And most of the micro – organisms are not free –
floating (as we may imagine in a culture tube) but instead grow attached to surfaces in complex communities called biofilms.
This is why we should build large bioconverters – to accommodate the various bacteria that will grow there.
estimated that the nitrifying bacteria colonize only a small portion of the media surface area. Some cells are able to produce
copious amounts of polysaccharides, which act as mucus layers and hold the cells to the surface.
These are called the
primary colonizers. This external slime captures other bacteria (secondary colonizers), who live and grow off the waste products
produced by the primary colonizers. Before you know it, there’s an extensive and complex microbial community, all tangled
up inside the polysaccharide slime. This is the biofilm.
ENVIRONMENTAL CONDITIONS FOR NITRIFYING BACTERIA
look at pH values, water temperatures etc for koi. Some experts quote a certain pH value as “ideal” for koi. But
lets look at the conditions that the nitrifying bacteria prefer and grow well in. after all these creatures purify the water
our koi live in. they are critical for the survival of our fish.
Nitrifying bacteria prefer an alkaline environment. pH
values below 7.6 – 8.2 are ideal for them. pH below 7 greatly reduces their performance. And at around pH 6 –
6.5 their activity stops. Above pH 9 nitrifying bacteria are also struggling. These bacteria prefer warmer water temperatures
of between 18 deg C and 28 deg C. The water environment is just as important for the nitrifying bacteria as it is for the
I find this interesting and perhaps a case against adding acid to try to lower the pH of our pond water. Over night
there is a natural decline in the pH. So when testing the water in the morning for pH do not be disturbed if it is lower than
in the evening.
However, if you add acid and there is a natural lowering of pH then you could have a pH crash on your
hands. This can be fatal not only to the koi but to the nitrifying bacteria in the bioconverter.
We mentioned above that
one of the characteristics of nitrifying bacteria is the fact that their food source has to be brought to them. This brings
us to an aspect of koi keeping that I consider one of the most important.
**IN PART 2 - FLOW RATES **