Trickle Tower Filtration
- Theory and Practice
by Bryan Bateman
AKCA Certified Koi Health Advisor
Vice President, MPKS
On our recent
trip to Japan, we became envious not only of the beautiful
Koi there, but of the practice of many of the breeders and
dealers there of not using any filtration. They utilize,
instead, "flow thru" systems. Bad water out, good
water in, using the never ending supply of crystal clear
water from the mountains above. This is a luxury that most
of us do not have. Instead, we must "re-use" our
water. This requires filtration.
There have been numerous
articles on many types commonly in use, but the long and
the short of it is that we have two tasks to accomplish:
removal of solids and removal of dissolved impurities. One
of the newer "kids on the block" for many of us
(the technology has actually been around a long time) is
known as trickle tower filtration. It is the purose of this
article to explain what this is, both in terms of what we
know about it and what we don't know.
Trickle tower filtration
essentially involves the flowing of water over a media where
bacteria live, converting ammonia to nitrite and nitrite
to the less harmful nitrate. The media is open to the air
and is not submerged in the water, thus providing the maximum
flow of oxygen to the bacteria while also encouraging the
release of harmful gasses such as carbon dioxide.
The normal conversion
of ammonia requires a large amount of oxygen, which is abundantly
available when the media and splashing water are exposed
to the air.
For this reason,
trickle filters are especially useful during the summer
months when the oxygen requirements of the bacteria as well
the fish are at their highest levels. Conversely, due to
the high exposure to the air and resulting evaporation and
chilling, these filters do not work well in colder weather.
As you may have gathered,
trickle tower filtration helps satisfy the second of our
filtration tasks - removal of dissolved impurities. For
this reason, it is important to use water that has already
had solids removed. Thus, the location of this filter would
be after some type of mechanical filtration. A simple type
of trickle tower filter could be a cylinder of sufficient
diameter - say 8 inches minimum - placed above a receiving
vessel. The cylinder is filled with most any type of media.
Sand or fine gravel would not work so well, as there would
not be enough "air space" within that type of
media for the oxygen to make contact with the bacteria.
Some better types of media would be pvc strapping, plastic
bio-balls, large pieces of lava rock, pieces of filter mat,
even hair curlers - anything that will remain loosely packed
with plenty of air space.
our system, we use five 12" diameter by 40" long
sections of pvc duct pipe left over from a project at work.
You could use a garbage can with the bottom cut out. Lots
of room for creativity here. In order to distribute the
water evenly over the top of the media, we use a 2"
diameter pvc pipe coming from a pump. This pipe has ¼"
diameter holes drilled every 2 inches. The cylinders sit
on a shelf which empties into a 500 gallon tank built from
landscape timbers and plywood, lined with rubber. Water
exits thru a pipe near the top and flows down a stream back
to the pond. This tank, incidentally, also contains the
coils for heating our pond water in the winter, so we have
a bypass allowing us to turn the trickle towers off during
the colder weather.
One question I have been asked is whether this type of filter
could be used in a closed system, such as a bead filter.
I can see two possibilities here. First, the filter could
be placed at the very end of the system immediately prior
to the pond return. This is essentially just as we have
explained above, and allows the towers to remain open to
the air. If, on the other hand, it is desired to keep the
trickle tower closed to the air, an air injection system
would be required.
creates two additional problems: how do we remove the air
prior to the water moving on thru the closed system, and
how to we get enough air into the filter to keep it an "open
air" and not a submerged filter. In order to work properly,
the water flow would have to be reversed - that is, upflow
rather than gravity (down) flow, thus taking advantage of
the tendency of bubbles to rise. Some type of pressurized
air valve would have to be installed to allow the air to
be released from the top of the filter. I leave the rest
of this design to some enterprising hydraulic engineer.
I understand that our British friends at Evolution Aqua
have been working on a closed-system version of the popular
Nexus system - a submerged but heavily aerated type of filter
that has gained a strong following in the hobby in recent
years. If they ever get that figured out, it could perhaps
be modified for trickle tower use.
We do know that trickle towers are highly efficient systems
for removal of ammonia and nitrites, and for gassing off
of harmful pond gasses. The nagging problem of nitrate removal
still remains. Although nitrates are not nearly as harmful
as ammonia and nitrites, this end product of the nitrogen
cycle can be problematic for the serious hobbyist who is
concerned with the optimal development of skin and color
know that certain plants can help keep nitrate levels at
bay. We also know that frequent water changes can be effective
if done properly. Nitrates can also be removed in an anaerobic
system, but this can have dangerous side effects.
is a fourth possibility - it has been suggested that trickle
towers will lower nitrate levels, perhaps even more efficiently
than any of the above mentioned. At this point it is only
speculative - not proven or explained by controlled experiment.
There are three possible ways that this could occur.
there could be isolated pockets of anaerobic colonies formed
in certain types of media such as lava rock or Bakki house
media - a highly porous log-shaped media used in Bakki shower
(similar to trickle tower) systems.
possibility is that nitrate, in the environment of the aggressive
"crashing" of water molecules against the media
as it falls, or some such similar phenomena, could convert
nitrate to nitrogen and oxygen. In other words, the nitrates
could be "gassed off".
A third possibility is that there may be a type of aerobic
bacteria which could thrive in a trickle tower environment
that actually would consume nitrates as a food source, much
the same way that anaerobic bacteria does.
Personal experience has shown that nitrate levels have indeed
been lowered when our trickle towers are running. During
the summer of 2005, our nitrate levels were hovering in
the 50 to 60 ppm level prior to running our towers. After
four weeks of running the water thru our five trickle towers
at a rate of about 3000 gallons per hour, the nitrate levels
in our 10,000 gallon system had been reduced to the range
of 10 to 15 ppm.
Was it a result
of the trickle tower? Or were there other factors at work
here, such as higher levels of algae, increased water changes,
etc.? Any way you look at it, trickle towers are an interesting
and efficient adjunct to any filter system. We continue
to use our original home-made horizontal flow bio-filter,
but will also continue to pump water from that into our
trickle towers. You just never know.
Bryan Bateman 2006