Mechanical filtration.
Most filter media have a mechanical function. Settlement chambers allow
gravity to drag the solid waste out of the water by slowing the water flow.
Such chambers usually come first in a filter. A vortex unit provides greater
settlement, the water moves in a circular movement allowing solids to gather
in the center where they can be removed. In addition to baffle plates which
slow the incoming water, brushes or matting can be used to strain the water.
Biological filtration.
This relies on specific bacteria to break down toxic waste products to
less harmful substances. There are two stages in the breakdown of ammonia,
each stage involving different types of bacteria. The first stage is the
breakdown of ammonia to nitrite by nitrifying bacteria, most important of
which is Nitrosomonas. The second stage is the conversion of nitrite to
nitrate by Nitrobacter.
Chemical filtration.
Activated carbon removes ammonia and other organic waste products by
adsorption, this means that the waste substances become linked to the
surface of the carbon. When the surface is 'full up' it has to be replaced.
Zeolite removes ammonia and nitrite from the water. A good feature of
Zeolite is that it can be cleaned by soaking in salt water (6g per litter)
for 24 hours and then reused.
If a large biological filter is present chemical filtration should not be
needed, but it is good to use while the biological filter is maturing or
isn't big enough for the pond.
Sand filter. Some Koi keepers use a sand filter as a final stage to
'polish' the water. The water is passed under high pressure through sand and
comes out very clear, bacterial activity also takes place in the sand
filter. Sand filters are expensive though, and you can't make one yourself
because of the high pressure involved. |
