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Bioseeding a new filter

One can understand the reluctance of authors to boldly introduce something completely different in books or magazines, because “labelling” can easily destroy a reputation. However, it is also true that the koi hobby would not have survived without a certain element of conservatism to imprint the basic principles of koi keeping in people’s minds. With the work done by pioneers in the koi industry, some innovative ideas have proven successful over time. Without this boldness, a hobby will stagnate. For example, many ideas have been borrowed successfully from tropical fish keepers as well as techniques employed by the marine fish fraternity. Just think about the use of ozone, UV sterilizers, protein skimmers, etc. Some things like underground filters employed in tropical fish tanks have been used in ponds for many years untill it was judged to be too risky. The principles employed by water purification works, are also frowned upon, but some koi keepers employ it with great success.

This article is not intended to create a vigorous debate about the merits and pitfalls of a new technique. The intention is to arm the Koi keeper with knowledge. Every reader should make up his/her own mind and then quietly do as they see fit. It is however thought provoking and I have employed it successfully in the past with excellent results.

Under normal conditions it takes up to six weeks for Nitrosomas and Nitrobacteria to settle in the bio filter and multiply to such an extent that it can remove/reduce all the ammonia in the pond environment. There are many variables and it is difficult to give a specific time for development of beneficial bacteria. Temperature and pH are factors that influence the time needed, and it is common knowledge that Nitrosomas start to grow immediately but initially not in sufficient numbers. There are those that advocate that a bio filter should go through all four seasons before it can be regarded as a fully matured filter system. There is no doubt that through the years the practical experiences of Koi keepers all over the world can adequately prove the above. The question is however, CAN ONE FIND A BETTER WAY?

Historically, we used to fill a pond, de-chlorinate, run the system for a few days, add new “canary fish” and observe if they survive or not. Then you add two fish per week so that the pond can slowly mature. That was the way to do it and any attempt to deviate was frowned upon by more knowledgeable Koi keepers. It was also commonly believed that the Nitrosomas and Nitrobacteria, even when settled in a bio film, would die off easily when exposed to chemicals or when disturbed. Furthermore it was regarded as part of the cycle (normal for the poor newcomer to the hobby) to experience “new pond syndrome” and although there are many theories and facts on why it happens, no one was able to offer solutions. The fact is that individual bacteria are very vulnerable and can be easily killed. They begin to adhere to all surfaces then multiply. As they multiply they excrete the slime that forms the bio films. Other organisms grow alongside them such as fungus and many other types of bacteria. Eventually you get your “Slime City”. Some years ago I read some very interesting references about clear water. Apparently the ammonia converting bacteria take up only a small part of the biofilm – the other microorganisms take up most of the space. Amongst the microorganisms population are the heterotrophic bacteria. They are the so-called organic munchers. These bacteria literally eat dead organics. They multiply in numbers and eat away the organics then they die back. The water clears and then seems to go through a period of murkiness. And the cycle begins again. The author of one of the articles asked why a pond became murky after the filter was cleaned and why ponds with smaller filters had murky water. He reached the conclusion that washing a filter, wash out some of the heterotrophic bacteria. He also concluded that small filters did not have the space to grow enough of these bacteria – his argument went further as he said smaller filters do not have enough nitrifying bacteria as these bacteria only take up a small area in the biofilm. Interesting, but at least this is the first indication that these bacteria can be dislodged, and this will form the basis of the technique described later. 

If one looks critically at these beliefs, a multitude of questions arose. For instance, if the pond was filled with sterile tap water and de-chlorinated, where do the bacteria came from? Some say it is everywhere in the soil and air, because it is the start of the nitrifying process in nature. Then you ask yourself how does this bacterium survive when the soil is dry and how can these vulnerable bacteria survive when airborne? If the bacteria only live in bio films, how can they become airborne? Why do you introduce fish gradually to a pond if this method takes much longer to mature as only a small percentage of the media surface will support a healthy biomass due to the low stocking rates? After all these questions, it is best to turn to more recent developments and discoveries and utilise this knowledge to the advantage of the hobby.

Some efforts have been on going to establish a biological filter in a shorter time than the “prescribed” six weeks or longer. One of the more successful methods is still to transfer some filter media of an established pond to a new one to give the pond and filter system a boost. To make an immediate impact will however require quite a lot of media, and if the fish is placed into the pond immediately, the chances of transmitting disease becomes a reality.

The other method is to take your chances and buy dry bacterial cultures that are available commercially. I have never seen it work, other that promoting the growth of existing bacteria. So it still leave us with the quest on how to establish a bio film in a new filter in as short a space of time as possible.

Peter Waddington wrote in his book “Koi Kichi” that the Japanese prepare their concrete ponds a week before they start harvesting. They cannot stock these ponds systematically if they harvest thousands of fish at a time. All these concrete ponds receive enormous volumes of stocks. However the key to this practice is the constant and expert monitoring of water conditions and the correct addition of new water to dilute the toxic waste products. He further states that within four to five days these systems are almost fully mature and feeding is carried out very sparingly over the next few weeks to allow all systems to mature fully.  Peter is convinced of and also applies the practice of substantial stocking of new ponds to create enough ammonia and waste material for the bacteria to develop at a faster rate. The above is not really in line with what we were taught!

Chris Neaves also explained in an article some years ago that his mature filter media was removed from his pond for weeks. It remained moist and when he placed it into a new pond, there were no ammonia or nitrite spikes. More recently he took us through the facts and fiction of filtration and also explains the “slime city” in more detail. It is very interesting to note that the “fragile” bacteria are in fact adequately protected once the bio-film is established. These bacteria colonies can actually withstand chemicals that we always believed would sterilise the whole filter. Click here for more info.

Some time ago, I also read how to mature a bio-filter by adding ammonia in controlled quantities to a pond until the filters are mature and then to stock the pond with fish. I cannot remember the source, but it claims to mature filters in a remarkable short time. After a final ammonia and nitrite test, the fish are released. The down side must surely be that the filter was able to handle ammonia and nitrite, but not a full biological load.

About a year ago, I got hold of “Koi Health and Disease” by Dr Eric Johnson. One of his articles finally changed my mind-set on how to mature an adequately filtered, but new pond.  It would seem like an impossibility that bacteria could be transferred to a new pond to create an instant equilibrium, but his technique made a lot of sense. After several experiments I can confidently state that this technique has been employed successfully in the very large pond and with common sense and proper aftercare, the dreaded new pond syndrome can be avoided. See some photos that we took while employing this technique at Charles and Marie Billing's pond.

How to go about it.

THIS TECHNIQUE CAN ONLY BE EMPLOYED IF THERE ARE NO FISH IN THE POND. If you try this in a pond with an existing population, they may die. Take some filter media carefully out of a healthy established filter and place it in a container. Add a few litres of pond water to the container and vigorously shake the media to dislodge all the brown muck and dirt. Repeat the process with more filter media until the container is filled with the brown sludge and dirt. This is present in any mature filter system. Now add an air stone and transport the container to the new pond.


The new pond must have a recipient filter, the water must be free of chlorine and the UV lights must be switched off.  Empty the container into the pond and watch in horror how the scum and muck distribute through the clear water.



This “activated sludge” is described on the Wikipedia web-site as an active biological material. This material, which in healthy sludge is a brown floc, is largely composed off saprotrophic bacteria but also has an important protozoan flora mainly composed of amoebae, Spirotrichs, Peritrichs including Vorticellids and a range of other filter feeding species. Other important constituents include motile and sedentary Rotifers. So for purposes of our discussion, the soup that you have poured into the new pond consists of dislodged bacteria, fish waste and a food supply for all those organisms that we know or even those that we do not know about. It is excellent for starting up a complete cycle. It is activated because it is oxygen rich and contains billions of microorganisms. It is worth its weight in gold as it is only found in mature filters. This material is distributed throughout the system and settles in the new filter. After a few days the water will be clear and the fish can be released into the pond.

There are two things to consider when employing this technique. The first is the question of disease. In relative warm water, the life cycle of pathogens are interrupted without the presence of a host fish. Therefore the waiting time before introducing the fish will depend on the water temperature. The second consideration is the fact that you are creating an instant biological load on the system and this create an immediate tax on the carbonates that uphold the pH. Therefore, you should supplement the carbonates in some way.

I have applied this technique several times when setting up new ponds without any negative effects or ammonia or nitrite spikes. I must admit that the fish that was stocked in this new pond all came from the donor pond, so I cannot confidently state that disease transmission will not occur when adding completely new fish to the pond. The risk is however much less than when you add mature filter media without a five day delay, and the pathogens present can immediately find a fish host and continue their respective life cycles.

Updated 18 June 2010


Last Updated on Monday, 16 December 2013 13:50