Koi Pond Filter Media KALDNES, Oxygen & Nitrification In Pond Water...

Kaldnes is a wonderful bio media - revolutionary in fact. For those of you with large garden ponds, and all you Koi pond fanatics out there that have existing filter systems, Kaldnes can be quite easily deployed as a significant bio filter 'upgrade'. You will notice I don't use the word bio converter much on the web site, since most people search for bio filter or biofilter!

But yes, Kaldnes is a bio converter medium on which bio film actively grows. The secret to using Kaldnes is in agitating it is some kind of vessel using large air bubbles to create massive volumes of turbulence. It is this agitation of the Kaldnes that gives it it's performance, although even as a static media it's not too shabby.

Kaldnes is a small plastic wheel, about 10 mm in diameter. It has a density very slightly lighter than that of water which means it tends to rise slowly to the top of a vessel in which the water is stationary. Add a little movement however and the Kaldnes tends to follow the water currents that are produced. The more turbulent the better because all the hundreds and thousands of little wheels then start bumping into each other.

Incidentally, you need between 20 and 65% density by volume of Kaldnes for optimum efficiency. This means a single 50l bag of Kaldnes is happy in a vessel of between 80 and 250l. Obviously, the bigger your initial vessel, the more Kaldnes you can add at a later stage and the more bio filtration, erm, conversion, you will attain.

The continual bumping and grinding of the Kaldnes against each other means that the bio film on the surface of the little wheel is under continuous attack from the other wheels. It gets scraped off and continuously has to renew itself. Whilst bio film is notoriously tough, this constant aggravation means that the colonies are active more than usual, which means that they are more effective in removing ammonia and nitrites from the pond water that passes through the system.

There is another very significant advantage to the Kaldnes 'moving bed' bio reactor. The whole process is conducted in an oxygen rich environment and it is one of the only systems that returns oxygen rich water back to the pond. This is an extremely useful 'side effect' of the Kaldnes moving bed process.

You can build your own Kaldnes bio converter easily and simply. All you need is a vessel of appropriate volume, an air pump, some tubing and Kaldnes. It is obviously easier to integrate this into a new pond when designing it from the very start, but even if you have an existing filter system this is an easy enough add on. It is best to create a vessel/chamber that can return water to the pond via gravity since Kaldnes does not work well in a system that is pressurised. It can of course, but injecting air can be problematic and the complexity of the system increases enormously.

Note that you have to ensure that none of the Kaldnes is allowed to escape the chamber. Stainless steel mesh with a 5 mm grid works well to cover your inlets and outlets to your vessel - believe me when I say that if Kaldnes is active - it is active! Give it the smallest opening (10.01mm!) and it will work it's way through the hole eventually and escape into your pond where your fish may try and eat it. Koi are not renowned for their brains.

An Airtech 40, 80 or 120 will do a brilliant job of providing large doses of big air bubbles that will turn your Kaldnes filter into a seething bubbling Jacuzzi pot. You add this air by running some tube around the bottom of your vessel, and poking a few small holes into the tub at regular intervals. Make these holes smaller rather than larger at first and I strongly suggest you experiment with a spare piece of tube before working on the final affair. A large pin sized hole is normally more than adequate - you want bubbles that are big and turbulent but not so big that the air pump can't keep up!

Anyway, that's my food for thought. Note that Kaldnes does NOT act as a mechanical filter - if you have no mechanical filter you should not rely on Kaldnes to be able to handle all your filtration. It is a bio media, and as such it deals with ammonia and nitrite (and even some nitrate) wastes primarily. The Answer is the mechanical filter device that should be used to help you rid your pond of all the waste that you can SEE.

Maintaining a balance in a koi pond, the nitrification process

These are the equations that of the reactions that the bacteria enable. Just take note of the large amounts of oxygen required.

For Nitrosomonas: 55NH4++ 76 O2 + 109HCO3- C5H7O2N + 54NO2-+ 57H2O + 104H2CO3

For Nitrobacter: 400NO2- + NH4+ + 4H2CO3 + HCO3- + 195 O2 C5H7O2N + 3H2O + 400 NO3-

What is important from these reactions is to note how much oxygen is used. Remember that dissolved oxygen is in limited supply in water and the warmer the water, especially in temperate climates like South Africa, the less oxygen dissolves into water. 4.3 mg of oxygen is consumed by the bacteria when converting 1 mg of ammonia into nitrates.

Warmer water means more Koi metabolism, more food, more waste, less dissolved oxygen in the warmer water - greater filter load the picture can quickly get horribly out of shape.

Also of importance is the effect on alkalinity. Gradually, pH will decrease as the pond becomes more acidic due to the production of nitric acid. This has implications for the water hardness and the pH stability over time. Koi ponds thus to regularly monitor water hardness and pH buffering capability.

Dissolved waste vs solid waste disposal

When the water is warm, Koi can excrete between 50 and 100 mg of ammonia per kg of Koi bodyweight daily. This starts to give us an indication of the size biofilter we need or more accurately the performance that is required by the bio filter. Sizing of bio filters is covered by one of my articles at www.happykoi.co.za click the articles link.

This is all well and good as far as the dissolved wastes produced by Koi are concerned. Of equal importance however are the solid wastes that comprise mainly of proteins and there is a great deal of solid waste that is produced when Koi are large and feeding as Koi do.

These solids if allowed to decompose also contribute to the ammonia load in the pond. Dead algae and other organic matter contribute to the ammonia generation process.

Solids removal in a Koi pond is NOT as simple as straining of the material. It is here that we first assess the viability of sand filters in a Koi pond.

A sand filter traps solid material very efficiently. The solid wastes that are trapped are almost immediately set upon by bacteria that break down these proteins into, you guessed it, ammonia! The general idea is to get rid of ammonia isnt it?

It is true that some nitrification might take place within the sand filter. Note I said some since in any location where there is oxygen, water and ammonia you are likely to develop a few beneficial bacteria.

However, as we already know, the nitrogen cycle uses 4.3 mg of oxygen per mg of ammonia produced. If protein decomposition is taking place in the sand filter by bacteriological processes (other than the nitrification bacteria there are many, many different types of bacteria in a Koi pond, not all of them good) then a good portion of the oxygen present in the water is going to be used right then and there in the sand filter by the nitrification bacteria (that do happen to be present) and the countless fast growing heterotrophic bacteria that are breaking down the solid organics.

This means less oxygen is left over for the bio filters that come directly after the sand filter.

Even then, can you see the big problem with black box bio filters? The only oxygen present to enable the reaction to take place is that is dissolved in the feed water that enters the filter at the start. Once this oxygen is used up, the rest of the bio filter has to make do without oxygen. These type of conditions are called anaerobic no oxygen and in these conditions there are a number of unwanted consequences that can arise.

Anaerobic conditions quickly become pathogen breeding grounds. Toxins from anaerobic breakdown of organic material can quickly accumulate, paralysing or adversely affecting other beneficial bacterial processes. Conditions for disease ripen and Koi immune systems are placed under considerable duress.

There are few conditions in any Koi pond where anaerobic conditions can contribute anything positive to water quality and hence Koi health. Sand filters in a Koi pond are a slow but sure death sentence. It may take a few years, but eventually Koi will pay a terrible price.

Solid wastes are bad news. Trapped solid wastes in the path of your filter cycle are even worse.

Look after your beneficial bacteria

It should be clear that as much as you look after Koi, you need to take care of the beneficial bacteria that contribute to keeping your Koi alive. You should minimise the potential for growing unhealthy or unwanted bacteria in your pond by staying away from anaerobic conditions as far as possible.

There are a few drawbacks to our beneficial nitrifying bacteria though. Unlike some nasty bacteria that can double in numbers every hour (think about the sand filter), these good bacteria grow very slowly. They are easily influenced by poor water quality (aside from high ammonia levels that is) and without oxygen will die off completely within 8 hours. It can take several months to re-colonise some bio filters with these bacteria.

Their required pH range is quite specific and is between 7.5 and 8.6 remember the acidifying effect of the nitrification process?

As with most living organisms their growth rates are affected by temperature and chemicals added to a Koi pond are likely to affect them adversely. Antibiotics will have predictable results!

Its a common mistake that filters need to be dirty in order to encourage the growth of bacteria. Whilst it is true that bacteria thrive under mucky conditions, its the wrong bacteria that grow. Fast growing heterotrophic bacteria end up competing with the slower growing nitrification bacteria for precious oxygen.

It is perfectly logical nitrification bacteria feed off dissolved wastes. Wastes that are visible to the eye are therefore not desirable food for nitrifying bacteria. Dirty filters are a haven for potential disaster since the heterotrophic bacteria that grow in them can and do easily produce by products from the breakdown of rotting organic material that inhibits the nitrification process either by direct toxicity or by creating a hostile microenvironment.

Dirty sludge filled filters are a no go in Koi ponds. If it smells bad, it is bad. In an ideal Koi pond there are no bad smells. Let your nose be a warning beacon of serious trouble!

The implication here is that filters need to be regularly cleaned and if they are constantly becoming clogged with solid gunge then this it true. They do have to be cleaned and this is indeed an unpleasant side to the hobby and represents a considerable maintenance workload for the Koi keeper.

The problem with cleaning the filter system is that some, if not all of the beneficial bacterial colonisation is destroyed, depending what stage of the filter system becomes dirty (the bio filter stage ought to never be dirty).

This maintenance can thus reduce filter efficiency until the colonies can re-establish themselves and this in turn places an ammonia load above normal levels in the Koi pond. Reduced feeding is one easy way to balance out the effects of filter cleaning but try tell a large hungry Koi that this is actually in its own best interests! It might also take weeks for the bacterial colony to fully re-establish and in a pond with a filter system that is only just coping with a full load, the possibility for disaster grows ever larger and more ominous.

Note that trouble can take years to manifest itself. As Koi grow larger, and the numbers of Koi in the pond remain the same, the load on the filtration system increases exponentially. A 60cm Koi places 8 times as much load on the filter system as a 30cm Koi does because it weighs 8 times as much!

William Kelly http://www.happykoi.co.za