Trickle Tower, The Perfect Biological Pond Filter


This time, I would like to talk over Trickle Tower Filter Theory after searching from various internet references worldwide, referring to either general water chemistry or any other experimental results conducted by several Koi enthusiasts as well as many arguments pertaining to Trickle Tower’s issues. To tell you the truth, I have not received an exact theory from any academic professors about what really happens on a Trickle Tower. Yet, it is the only type of biological pond filter that can reduce nitrate (NO3) significantly.
Acknowledgments I dedicate on Mr. Google that has guided me to find many valuable references over Trickle Tower experiments unnecessarily conducted by me myself. :). One of main URLs is found at this forum where Mark, a pond enthusiast, had initiated to reveal out some of his Trickle Tower experiments completed with corresponding measurements.
Now, let’s move on to the lesson...
A. How to Manage Clear Pond Water
To clear pond water needs only 3 requirements:
  1. Free from debris
To get rid of this, the necessary mechanical/physical treatment must be available, namely:
a) Settlement chamber, usually in the form of a vortex chamber, to settle heavy/hard debris,
b) Japmat, filtermat, or brush, to catch the flying debris that can not be settled in the vortex chamber, and
c) Fine Debris Filter Mat, the final physical filter, to clean out fine debris.
  1. Free from dyes
Dyes in this term here mean anything that can cause water to be discolored (reddish, bluish, etc). The mayor cause is mostly by fish food type and excessive feeding. Therefore, it is wise to avoid excessive feeding and select good fish food that does not cause discoloration to the pond water. There is no special way to get rid of this, but along with the oxidation occurring all the time in the pond, usually the dyes are then bound with other bigger molecules and consequently trapped by the fine mechanical filter chamber.
  1. Free from algae.
In a relatively high concentration of either ammonia or nitrate in a pond water, with the support of sunlight, can cause the pond water to become greenish due to alga bloom. As algae are microscopic, they could not be filtered through any existing mechanical filtration chamber. We do not necessarily have to kill the algae, instead, we’d better prevent the algae not to grow well in our pond, by minimizing the concentration of both ammonia and nitrates from the water by the so-called biological filtration which will be talked over below.
B. Nitrate, The Final Substance of Nitrogen Cycle?
In the biological nitrogen cycle of conventional submerged filtration system, fish waste products in the form of ammonia (NH3 and NH4 +), are then decomposed into nitrite (NO2) and subsequently converted to nitrate (NO3). All the liquid nitrogen compounds of the ammonia, nitrite, and nitrate contain several molecules that have some bonds with the nitrogen elements. These compounds have to be maximally removed for effective filtration result. Decomposition of ammonia to nitrite and subsequently to nitrate takes place in an aerobic condition (oxygen needed) whereas nitrate takes place in an anaerobic one. The biological decomposition of both ammonia and nitrite along with oxygen generally occurs with the help of some bacteria namely Nitrosomonas sp (oxidizing ammonia into nitrite) as well as Nitrobacter (oxidizing nitrite to nitrate). Both Nitrosomonas and Nirobacter live by attaching themselves onto any solid objects, the more extensive the contacts the more effective biological filtration takes place, following the chemical equalities:

4NH3 + 7O2 ---(nitromonas)---> 4NO2 + 6H2O
2NO2 + O2 ----(nitrobacter)---> 2NO3

Aerobic process is more easily done in the filtration system rather than of the anaerobic one. Just aerate the pond water and let the bacteria do the filtration process themselves along with the media such as bioballs, japmat, or filtermat. Usually such system would result in nitrate as the final compound. The Nitrate is too difficult to decompose as it must be on an anaerobic condition. Also reported that the anaerobic condition of a pond circulation system has the potential to make fish population susceptible to disease, the reason why such treatment is rarely conducted. One popular filter example that uses the decomposition of nitrate is known as "coil denitrator", which is usually applied only for the aquarium water treatment usually following the chemical equation:
2NO3 --- (anaerobic )---> N2 + 3O2
For any koi pond, the above reaction is hardly conducted considering the large amount of pond water, so that the nitrate can relatively also be hindrance for the koi enthusiast.
Please note here that the biological filtration needs a relatively long time due to the process of bacteria 'eating' ammonia to produce nitrite and subsequently nitrate. The term biological filtration means that the bacteria process the nitrogen compounds by means of their own digestive bodies, so it can not happen in just a short time. That’s why, based on general rules that may have been tested by conventional koi experts, there has been a consensus which says that effective submerged filter volume is supposed to be 1/3 of the main pond water volume. This is, nothing intended, in my comprehension, in order that the water runs pretty slowly on the sidelines of japmat / bioballs so that there is enough time for the nitrification and denitrification bacteria to decompose ammonia to nitrite and then nitrate.
Despite nitrate is not really harmful against koi fish, however, in an excessive level, it can decrease the Koi’s growth as they should. In addition, nitrates can also trigger the growth of algae as well as moss that can cause pond water to become greenish. Conventionally, to reduce/dilute the nitrate level, the pond owner during a certain period, need to make 20-25% pond water change with the fresh one. A practical way to get rid of the problem, but is boring if managed everyday. :)
Another way to lower nitrate level is to give the so-called Veggie Filter (vegetation filter). But it does need both a relatively broad area and sunshine as well in order that the filtration runs effectively. Besides, fallen leaves must be cleaned soon so that they don’t sustain contribution of ammonia and dirty/clogged water ponds. Off course, such filter is not suitable for those having limited space.
C. Trickle Tower Theory
Actually the discussion about Trickle Tower has grown long enough, either by pond or aquarium enthusiasts. But the controversy about its use, so far, was not really complete in the theoretic scope. There are some quite fundamental arguments by experts regarding the trickle tower issues, whether it can remove or even produce nitrates (i.e. the final result of Ammonia-nitrite-nitrate decompositions). However, some other enthusiasts proudly announced that their DIY Trickle Towers are much more effective to break down fish waste rather than the submerged ones. What a nitrate remover!
In the subsequent development, Momotaro Koi Farm had attempted to perfect conventional trickle tower with a new name of Bakki Shower, which mainly differs in their 4 tray system. Which of these filters is more effective? Later will be explained.
There are 3 possible reactions happening regarding the capability of Trickle Towers releases the nitrogen molecules into free air:
1. Aerob Reaction
The gaseous nitrogen molecules can be released from the waste compounds (Ammonia, Nitrite, and Nitrate) by some kind of bacteria (aerobic or anaerobic) through an excessive oxidation process converting nitrite into NO as well as (in greater amount) N2O which is 1,5 times heavier than the air. It gives the comprehension that in the waste nitrogen compounds to release gaseous nitrogen molecules, the nitrite becomes the gateway of the process. Shortly speaking, before the nitrate is formed, the nitrite precedes to react with the remaining ammonia to release nitrogen molecules into the air. Even for the available remaining nitrate itself, it has to be converted as well into nitrite so that the reaction could take place. You can’t do it, but the bacteria can!
As a matter of fact, in the conventional submerged system, both NO and N2O can still be produced and ready to be released into the free air as a proper process. But due to both the lack of aeration and the difficulty of the molecules to escape out of the filter chamber, the both gaseous nitrogen molecules NO and N2O would then re-react back with the water (H2O) resulting in new soluble nitrite and nitrate which subsequently re-circulated into the pond circulation system. What a pity!
A natural example of an excessive oxidation condition occurs in water river flow. With so many cracks among the corals can cause the water to become clear, away from the greenish impression of algae.
2. Anammox Reaction - (Anaerobic Ammonium Oxidation)
In biological processes inside the trickle filters, both nitrite and ammonia are converted into gaseous nitrogen by following the reaction:
NH4+ + NO2- à N2 + 2H2O.
The bacteria that perform this process are including the phylum planctomycetes and Pirellula. Excessive oxidation here is used to convert some of Ammonia to nitrite (NO2-) and subsequently react with the remaining ammonia in aerobic conditions. Pay attention that there is no nitrate produced. The whole both ammonia and nitrite react each other to release N2 and pure water.
3. Excessive Oxidation Reaction
Based on an experiment conducted by Mark, say the pond expert, with 4 tons of pond water, using submersible pump of 25 tons/hour, and the capacity of the former submerged filter containing 1200 submerged bioballs, he managed to reduce nitrate concentration from 250 ppm to 10 ppm in his pond just within 6 days.
If we understand, the water that passed through the cracks of bioballs on Mark’s above experiment, due to the large water discharge, the water flowed so fast that it was almost impossible for bacteria on the bioball’s surface to be able to decompose the whole ammonia contained in the water. What definitely took place then was that the water spread through bioballs would increase oxygen level significantly (excessive oxidation) so that it made gaseous nitrogen molecules, either in the form of N2, NO, or N2O, to 'vaporize themselves', escaped from ties with the waste compounds of Ammonia, nitrite, and nitrate.
Relating to excessive oxidation mentioned here, there are two possible analysis to take into account:
a) Without any Biological effect:
By means of excessive oxidation, it is likely to release molecular nitrogen in the form of gas from the three waste liquids of ammonia, nitrites, and nitrates without undergoing any biological process, but just excessive oxidation taking place. It is also based on the common fact that the concentration of nitrate will be relatively low in the pond water where good oxygen contact is available.
b) With Biological Effect
In case of a mature pond, biological equilibrium actually has already been taking place, since the water kept circulating as a result of natural nitrogen cycle. The dissolved ammonium-nitrite-nitrate in the form of ions circulating throughout the mature pond, need the right place where excessive oxidation occurs to release the gaseous nitrogen molecules. The Trickle Tower does enable such circumstance.
D. DIY Trickle Tower Best Design
Keep in mind that each theory aforementioned does contribution towards Trickle Tower’s perfect filtration result. All we could do now is to breakdown and accommodate the above three reactions into an ideal DIY trickle tower design. By doing so, hopefully our own Trickle Tower design would work well supporting the purpose “small pond for many fish” or “kolam kecil ikan banyak” in Indonesian. Let’s try…
1. Well Ventilated Base;
Referring to figure 1 exposing that N2O is 1,5 times heavier than the surrounding air, so that it tends to settle at the bottom of the filter chamber, therefore it is strictly recommended that the bottom side of the trickle tower chamber is supposed to be very well ventilated (open). Such design will allow the heavy N2O to escape out by the environment breeze blow. Otherwise, it is not impossible that some of the N2O produced would again dissolve in main pond water to form new nitrate, back into the pond to circulate again and again. That’s why, when referring to this theory, a good trickle tower is not supposed to own trays as seen in a Bakki Shower. We’d better let the water pass through the cracks of bioballs without any tray hindrance.
2. Water Spread
The thinner the water wets the solids, the better the oxidation takes place. This can be conducted by spreading the water feeder towards large possible surface. The water trickles should not be too rapid to allow ‘wet and dry’ condition throughout the whole bioballs as ideally called for.
3. More Bioballs
The larger the solid surface, the faster the nitrogen compounds to be degassed from the liquids of ammonia, nitrite, and nitrate. In case of solid materials installed, I personally recommend to use bioballs as the medium that have very large surface area and are not easily clogged. The more the bioballs, the better the biological filtration. Just use Mark’s overview by using 300 bioballs/ton as minimum calculation.
E. Trickle Tower’s Controversy
Some aquarists maintained that Trickle Tower seemed to be a nitrate producer. We may say that this is likely due to the lack of air circulation inside the Trickle Tower. Remember that they usually locate the aquarium tank inside the house, don’t they?
On the other hand, koi ponds are usually located outside the house where the breeze will blow the gaseous nitrogen waste out of the Trickle Tower. So, we can conclude that aquarium’s trickle towers are different from those of the ponds due to the filter’s location.
We could give them advice for those who use the trickle tower as the biological filter:
Try to give good aeration throughout all bioballs to ensure that gaseous nitrogen molecules can easily escape from the tower by installing small electric fan at a strategic position, so much so, the waste gas emerging could be released at once. This manner also would avoid the gaseous nitrogen molecules re-reacting with the water and consequently reduce the nitrate level.
Hopefully my comprehension from various references on the internet is useful for you. Do give me suggestions and critics to improve the theory of The Trickle Tower for our own goodness.

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