THE INS AND OUTS OF KOI POND BUILDING
by Mike White, White Water Filters
Part 4: Mechanical and Chemical Filtration
In this article
we are going to discuss filtration. Filtration is broken down into
3 different types; mechanical, chemical and biological. I will be
discussing each type in detail. This article will cover mechanical
and chemical filtration with biological filtration to be covered
in the next article.
To begin, we
will cover mechanical filtration. Stated simply, mechanical filtration
removes debris or compounds from the pond through a mechanical device.
The device could be as simple as a net or as complicated as a foam
fractionator. Every mechanical filter has a specific purpose. When
looking at mechanical filtration it is important to first identify
what you are trying to accomplish and then choose the correct product
for the solution.
on a pond we see a skimmer; which is a mechanical filter used to
remove floating debris from the surface of the pond. Within the
skimmer there are usually two different devices. First a weir designed
to take water from the surface. Next a net or basket is used to
collect debris. When looking at mechanical filters, we need to analyze
how well it will do what it is intended to do. Using our skimmer
example, let's break down how it is supposed to work and determine
what to look for in a skimmer.
The first thing
a skimmer is supposed to do is remove debris from the surface using
a weir type device. Water is intended to enter the skimmer by going
over the top of the weir that floats so that only a thin layer of
water goes over the top. Therefore, any water that enters the skimmer
opening by not going over the top is a waste. In this way we can
get a good idea of how well it will work by looking at its construction.
use a door that is hinged at the bottom. Yes, water will go over
the top as long as the amount of water being pulled in is more than
the amount of water going under the door and along the sides of
the door. If the skimmer has an 8 inch weir with a ¼ inch
gap around the door, the area of the gap would be approximately
5 square inches. That is almost the same amount of area as a 2 inch
pipe. This is with the door shut, but as the door opens, the gaps
on the sides get larger and less water is drawn from the surface.
With the door shut as much as 1000 gph can go around the door before
it starts to take water from the surface of the pond.
The second part
of the skimmer is the net or basket that catches debris. The first
thing to look at is whether the net or basket is going to catch
all the debris entering the skimmer or can some of the debris get
past without being caught. Also make sure the holes in the net or
basket are the correct size to catch the debris you are trying to
remove from the pond.
Every pond should
have at least one mechanical filter and usually more than one. Not
every mechanical filter is easily examined to determine if they
will indeed perform the work they are intended to perform. A good
example is a foam fractionator or protein skimmer. Their purpose
is to remove dissolved organic materials from the water. One problem
is that you can't see these materials so how do you determine if
the device is going to work? Even though you can't see them, you
can see the effect they have on the pond water. The dissolved organic
materials will cause bubbles on the surface of the pond to take
longer before they break. With this knowledge we can determine how
well the foam fractionator is working.
Next let's cover
chemical filtration. Chemical filtration is accomplished by adding
a chemical to the water to remove some substance from the water
or tie it up so that it is no longer harmful. Chemical filtration
has a limited use in that once the chemical is used up it no longer
has an effect on the water. Chemicals used for this type of filtration
can range from dechlor to ozone.
As with any filter
you should first determine what you are trying to remove from the
water. You then select a chemical to address that problem. In some
cases it is important to know the volume of water you are trying
to treat or the amount of the substance you are trying to remove.
Sometimes if too much of a specific chemical is added it might poison
the pond life. It is also important to know that in some cases once
a chemical is added to the pond water, it stays in the water until
it is removed or used up. Many chemicals do not dissipate in the
water and they don't evaporate. Because of this, when you add different
chemicals in the future you may have a chemical reaction between
the two that could result in undesirable or harmful conditions.
Removing one chemical from the pond is not easy. It can be removed
by water changes but to remove 99% of the chemical by water changes
would take a change of 8.9 times the volume of the pond. For example,
if you changed 5% of the pond volume once a week it would take 178
weeks to get 99% out. That is approximately 3 and a half years!
The same would hold true for medications.
A word of advice;
be careful of anything that you put in your pond because it might
be there for a long time. Of course there are some chemicals that
disappear fairly quickly. Ozone is one of these. It has a half life
of 4 minutes in ideal conditions and much less in any other conditions.
What, you ask, is ozone and what does it have to do with a pond?
As ozone is one
of the newer ideas being used in the pond world I will explain it
as simply as I can. Oxygen normally forms molecules as two atoms
of oxygen (O2) but ozone is one molecule of oxygen with three atoms
of oxygen (O3). Because the third atom of oxygen, ozone is always
trying to get rid of that third atom. Because of this it is a very
powerful oxidizer. In fact it is the second most powerful oxidizer
known to man. How does that apply to a pond? It means that it can
oxidize any organics in the pond. In fact it can be so efficient
at oxidizing nitrite to nitrate that the bacteria that would normally
take care of this can die off due to a lack of nitrite for them
to eat. A word of caution, ozone can be a very dangerous compound
and should not be used unless you know what you are doing.
As stated earlier, the next article
will cover biological filtration.
1 - Planning a New Pond || Part
2 - Design || Part 3 - Circulation
|| Part 4 - Mechanical and Chemical
Filtration || Part 5 - Biological
Filtration || Part 6 - Biological
Filters - Mats, Pads and Biofalls || Part
7 - Biological Filters - Bead, Tower and Vortex Filters || Part
8 - Fluid Bed, Bio-Reactors and Nexus Filters || Part
9 - Planning for Pond Expansion
©2004 all rights reserved to Mike White