Malaysian perspective on pond filters
purpose of this insertion is to highlight the essential features a
pond filter should incorporate for an efficient filtration under the
hot Malaysian tropical climate. Some of the views may contradict what
I have read in the forum and other websites. This is an attempt to
give another perspective, so that would be ponders can decide what
systems suit their needs.
is no right or wrong way of pond filtration; it is a matter of what
suits you best and how much you wish to spend. Most of the time it is
decided by the availability of equipment in your area.
I must qualify by
saying that I have not experience snow and therefore have no knowledge
how the filter works during winter. Therefore this discussion may not
apply to cold whether.
The biological process
Before we go into the
process of treating fish waste, lets look at how we treat our own
waste. There are lessons to be learned here, since the food that we
consume is not too different from koi.
If your home were
not located within a housing estate most probably you would have a
septic tank. The septic tank consists of two chambers, the intake and
discharge chamber. A buffer plate at the top separates the two
chambers. This buffer plate blocks all floating waste from escaping
through the discharge pipe. The bottom of these two chambers are
linked; this is where all the waste accumulate and the biological
process taking place. One
can expect this is not a very efficient process. The only oxygen
available is from the dissolved oxygen in the flush tank. Once the
dissolved oxygen is depleted anaerobic process took place. This
process is manifested by production of hydrogen sulphite gases, which
emit a rotten egg smell.
authorities have adopted the more effective method; developers are
required to provide oxidation ponds to treat sewage. An oxidation pond
takes in fresh waste from the intake chamber. An agitator is used the
break up solid waste into small fine pieces. It is them pump into the
main pond. Oxygen is provided by large size aerator and also through
water surface. Biological process took place in the main pond and
sludge settles at the bottom. The initial assumption that sunlight may
help in the biological process by encouraging algae growth, which
feeds off the waste proved to be insignificant. At the far end of the
oxidation pond is the discharge outlet. This process proved to be more
efficient and one can find tilapia fish breeding in most oxidation
the appreciation of land prices, small efficient plants were developed
to maximize land use. These plants do the same job as oxidation pond
but occupy only a fraction of land required. I had the opportunity to
install an automation system in one of the plants a couple of years
back. The process is quite simple; waste is broken up at the intake
chamber. It then leads to a long aeration chamber. Oxygen sensors are
placed at strategic locations to monitor the dissolved oxygen level.
The dissolved oxygen level regulates the number of aerators turn on at
any time. After the process, the waste is then lead to settlement
chamber and then discharge outlet. Lately, the design has been
improved; the aerator has been replaced with air diffuser that can
produce very fine bubble.
all the above systems, there is no filter material. That is exactly my
point; the biological process goes on in the complete absence of
filter material. You do not need filter media to roost the bacteria
and have biological process. After the seeding and startup of the
plant, the bacteria is everywhere, in the water, but mostly attached
to waste particles, walls. But wait do not go and rip up filter media
just yet, I shall return to continue.
I stated that the
biological process goes on in the complete absence of filter material
by illustrating the process that goes on in our sewage treatment
plant. Many of you may not believe that the treatment process is that
simple. I do not believe it myself when I crawled into one. If you
have a chance, go visit one there are things we can learn. However,
please have a guide to bring you, on occasions poisonous fume have
been found in the chambers.
design variations in each sewage treatment plant are always in the
intake chamber. Some plants degrit the waste to strip bio waste clear
of other waste like paper and other stuff we throw into the toilet.
The less degradable waste would be separated and discarded to extend
the duration between each desludging. In all instances the only
process that goes on is to aerate the waste, either by aerator or air
diffuser, manually monitored or completely automated. No filter media
I have not convinced you that we do not require filter media to roost
the bacteria, here is one more try. I may need Biologistís help
here. Bacteria is not visible to our naked eye, the fish waste is. One
can imagine the number of times each waste particle is greater than a
bacterium. To think of bacteria attaching themselves to bio balls or
Japanese mats and taking a bite as each particles of waste comes along
defies my logic. In my shallow knowledge on biology, I believe
bacteria do not have well formed mouthpiece like we do. It also defies
logic to imagine that invisible bacteria could attach itself to filter
media and stretch out lengthening itself thousand of times to bite any
food that flow by.
only possibility is for the bacteria to attach itself and form
colonies on the waste particles. Ingesting food and reproducing on the
waste particles itself. This scenario must happen in the sewage
treatment plant in the complete absence of filter media, the only
possible way for the waste to be processed. Can I also conclude that
the same process has to take place in the mud ponds, lakes and rivers?
you are still not with me on this point, fine, no love lost. At least
we could agree that we still need filter media to trap all the waste
and algae to make our pond sparkling clean. Whether the bacteria
attached itself to the filter and taking bikes off the waste particles
or the bacteria form colonies on the waste itself is of no relevance
to the following discussion.
we do not need filter media to have biological process to take place,
why have we been using it for years? For two reasons:
1) To trap all solid particles, waste, algae, so that our pond
water could be sparkling clean.
2) This is my unproven thought; no scientific paper published;
none intended but logical. The fresh waste in the pond takes time to
be seeded with bacteria. This is because in the pond, the
free-floating bacteria are fewer in number. It takes longer time for
the bacteria to be attached to fresh waste particles to start a
colony. In the matured filter media, there is high concentration of
bacteria colonies formed on old waste particles. When fresh waste is
drawn into the filter chambers, they are brought into contact with old
particles and get seeded quickly with bacteria, thereby started the
biological process. In other words it means, so long as there is a
place where the fresh waste particles could be brought in contact with
old wasted particles, bacteria colonies would form on fresh waste and
start the biological process. It is immaterial how and where the fresh
waste is brought into contact with old waste particles.
I also conclude now that the different types of filter material used
in filter chambers, its shape and colour do not have direct influence
over the speed of biological process, provided that these different
filter material has the same capability of trapping waste particles,
all things being equal.
do not rip out your filter media just yet, we still need them, but you
may have to later if you are having green water at the moment.
The Principle of FILTRATION
water purification filtration technology, we are concerned with
filterability of media, the ability of a medium to filter and trap
solids. Fine silica sand is capable of filtering solids down to 5
microns size. Anthracite, having more uniform particle size is said to
principle is simple, if you have a more densely packed material the
better it would trap solids, the cleaner would be your filtered water.
However, it is also equally true that if the filter media is more
efficient in trapping solids it would be harder to clean and dislodge
the trapped solids. No magic here, for a filter media to be efficient,
it must be capable of trapping the solids and would not allow the
particles to be dislodged easily.
following filter media are generally used and available locally.
After Filter for water polishing
(7) Sand Filter
(6) Green Mat
(5) Ceramic Rings
like to note that eventhough these are the materials generally
recommended for used in each of these chambers. There is no law to say
it must be so, you can choose to use any of these materials in any
chambers to achieve the objectives you intended.
number infront indicates the filterability of media. The higher the
number the better it would trap waste particles. Voltex filter and
Trickle filter are not rated, they deserved to be discussed
avoid any confusion, Japanese Mat I refer to here is the fibrous type,
which comes in green colour about 1 inch thick. There is also a blue
colour version, which is 1 ľ inch thick. The Green mat, I refer to
looks like compressed nylon wool. The type of nylon wool we used in
our small overhead aquarium filter.
is not my intention here to write about the details of filter chamber
constructions. There are various articles on this website and good
number of books written specifically for koi ponds and garden ponds.
If you have constructed your filters as per recommendations, and there
are no problems. Congratulations, you have done it right. If you are
facing the green water problem, or high nitrite and ammonia problem.
Here is where I can help you with some solutions. It makes me very sad
to hear anyone can only feed his koi once a day or no feeding to
arrest the problem of high nitrite/ammonia.
shall tackle the problem of pond water clarity and high
nitrite/ammonia problems separately. However, one should not conclude
that if we solved one problem the other problem would be solved
automatically. They are separate problem though interrelated.
Pond water clarity
a hypothetical situation. If you are feeding koi with 300 gm of
pallets a day. You can expect to have almost the same amount of waste
introduced into your pond everyday. The weight of nutrients absorbed
by the koi for growth and organ functions is negligibly small and for
our discussion purpose is excluded. In every 10 days you would have
close to 3 kg of waste generated. A portion of the waste would have
dissolved in water as dissolved organics and various other salts. How
much of waste trapped in the filter material is dependent on the
filterability of the media. If your filter media is porous and loose
you can expect a large portion of waste particles to escape through
the filter media and back to the pond.
would not expect your pond water to be clear, would you?
the total volume of filter material in your filter system is 1 cubic
meter, every 10 days you would have 3 kg of waste to trap. If you are
using only nylon brushes now, possibly after 10 days, your filter can
only trap 500 gm and get saturated. The balance 2.5 kg is in the pond
clouding the water. To achieve clear water, you must have a larger
filter with total 6 cubic meters of nylon brushes to trap all 3 kg of
waste. Not forgetting to mention you would also need to flush and
clean the nylon brushes before it gets saturated with waste.
most instances, it is not possible for you to enlarge your in-ground
filter size. The other alternative would be to use finer filter
material say 1 cubic meter of green mat stacked all together. The
green mat would be able to trap all of 300 gm of waste generated
everyday and give you clear water. Unfortunately, the interstice space
of green mat is very small, possibly would saturate after trapping
only 1 kg of waste. In this case though green mat could solved your
pond clarity problem you need to flush them before every 3 days for
them to keep working.
other words, to solve your present pond clarity problem, there are two
options. One, using the same filter media and enlarge the filter tank
to increase the volume of filter media. Two, use filter media with
better filterability but compensate with more frequent flushing to get
rid of trapped waste particles before the filter media saturate and
allow the waste particles to escape back to the pond. If you have your
filter media in the bio chambers spaced out, leaving a clear water
passage between each layer; you just reduced the filterability of your
filter media by a good 50% to 70%.
is unfortunate that I am not able to obtain any data from filter media
manufacturers to state the recommended amount of waste it could trap
before saturation or the percentage of waste particles it could trap
in one pass. If we have this data, it would take the guesswork
completely out of our design. Until the manufacturers run tests and
publish such data, we have to do it by trial an error. If you have not
started digging, please over-design your filter size to avoid future
the above discussions, I have not brought the pond size into the
equation. From the filtration point of view, it is immaterial whether
your pond is 10 ton or 100 ton. If you could trap all the waste
generated everyday, you have a clear pond water. However, from the
health and growth potential of koi standpoint, you have to follow the
recommendations of experience hobbyists and breeders to decide on
if you have a larger pool of water, it would have larger buffer
against temperature, PH, nitrite, nitrate and ammonia fluctuation.
other consideration is in the event of a power failure what is your
likely response time for you to get back from your work to start up
your standby generator set, if you have one. If your stocking rate is
very high either reduce it or you better equip yourself with an auto
startup and auto changeover generator set. Or at least hook a few air
pumps to UPS to avoid heavy casualty in the event of power failure.
you had followed the recommendations on the filter design and your
pond is having green water problem, there are two possibilities:
1) New pond syndrome. If your pond is new or you just have a
complete change of water, as the pond matures, under certain water
conditions algae will bloom. In my case it has nothing to do with high
nitrate or inefficient filtration. After I turned on the UV light for
4 days, water turned clear and I never have to use it again. The
nitrate concentration in my pond at the moment is 25 mg/litre much
higher compared to the time when I experienced algae bloom during new
2) If your pond is more that three months old and looks green,
most likely it is due to your filter. Any particles escaped from
filter will be in the pond, with strong sunlight; algae will grow on
the waste particles making it looks green. If you have a pond full of
these green particles, your pond water will look green. High nitrate
could of course worsen the problem.
The second green water problem could
arise from two possibilities. Insufficient filter media to trap waste
particles or filter media could be over saturated with accumulated
waste. If you have not experience green water problem before and now
the water turns green. It is very likely that your pond filter is
saturated and requires cleaning. Observe the period you have this
problem and workout a schedule to clean out each chamber in sequence.
Never clean out all the chambers in one operation, otherwise you would
not have any bacteria left to seed the new waste.
If you have the
green water problem from day one and the same problem persist after
few months. There is only one thing left to do, rip out your filter
material and replace with more dense material or enlarge your filter
size. If you change your filter media to a denser type, you should
also shorten the period between each clean out. If in your bio
chambers you had left a clear water passage between each layer of
matting, plug it up. Water clarity will improve. However, there is
disadvantage in doing so and I will explain below.
High Nitrite/Ammonia problem
It is possible that
you may have a crystal clear pool of water, but suffers high
nitrite/ammonia problem. The reverse is also possible. I will explain.
in the pond continues to discharge ammonia day and night.
bacteria require oxygen to convert ammonia to nitrite and from nitrite
oxygen is depleted the bacteria will die off, the process stopped;
concentration of nitrite and ammonia will increase. To avoid this
problem all you need to do is to ensure all the aerobic bacteria has
sufficient oxygen, simple as that. It is mine believe that if the koi
can survive on the dissolved oxygen level in your pond, so can the
aerobic bacteria. I for one truly believe that aerobic bacteria can
survive under quite deep water. In all the sewage treatment plants I
have seen, they range from 1.5 to 2.5 meters deep. My in-ground filter
is 6 feet deep but well oxygenated.
high ammonia/nitrite problem arises from within the filter media.
Aerobic bacteria are invisibly small and they need to be in constant
contact with oxygenated water to survive. Within the filter media, as
it traps waste particles the waste particles built up forming a thick
layer of paste like waste sticking on the filter media. Aerobic
process could only occur on the surface of thick waste and within the
waste itself, in the absence of oxygen, anaerobic process occurs.
filter is particularly susceptible to anaerobic conditions. When new,
the gravel filter traps a lot of waste in the crevices. As each pocket is filled up, water will divert and flow to an
easier path depleting oxygen supply to the waste trapped in the
pocket. Anaerobic situation occurs.
media like carlnet and nylon brushes will not permit high build up of
waste. When the waste gets thicker, water current will wash it off to
the next chamber. These material are not likely to encourage anaerobic
process. However, carlnet and nylon brushes are notoriously
inefficient in trapping solids. We have a delicate situation here,
material efficient in trapping waste could create anaerobic condition,
and material good for aerobic process are inefficient in trapping
Optimum Filtration System Design
have clear water in the pond by having an efficient filtration is not
the only consideration. It must also keep the water parameters within
acceptable limits. One can overcome the murky water problem by
increasing the efficiency of the filter in trapping solids, however,
it would also mean you must monitor and shorten the period between
present filter system design though in use for many years and by many
koi enthusiasts is flawed in design. Instead of using nylon brushes in
the first chamber and allowing 90% of the waste to be trapped and
processed in the bio chamber. The ideal filter would be to trap 90% of
waste in the first chamber and discharged it on a daily basis leaving
only 10% waste to be processed in the bio chamber. This would truly be
a low maintenance efficient filter.
present filter upgrade will be based on this concept. I shall keep you
inform in six months if it is successful.
the next article I will share with you the Design Concept and
Selection of Voltex Filter. This will not be an advertising material
but a DIY concept to help you construct your own Voltex filter. Give
me a couple of weeks.
you have any queries on the above please pose your question in the
forum. If I missed please send me an email. Just do not ask me on koi
medication and tategoi selections, still paying very high school fees
in learning. Paying for tategoi getting a mutt.
Please post it at the Koi
Forum if you have any comments