A biofilter has one single function... to purify fish
excretions
(contain ammonia) which are part of the natural respiratory and
feeding function OF POND FISH OF ALL TYPES.
Pond Filtration: The
Basics
By Dave
Kelly
Want to know why creating healthy,
low-maintenance ecosystems is so important to contractors who
install naturalistic watershapes? It’s because the last thing any
of us needs during the busy season is a phone call complaining
about murky pond water!
To be healthy, a living ecosystem needs plants, fish, aeration,
rocks and gravel, but to help keep the water clear in the vast
majority of ponds, there must also be an adequate filtration
system.
Three types of pond filters are available on the market: biological
filters, mechanical filters and sterilizing
units. Biological filters use bacteria to break
down pond wastes, converting them into less harmful compounds that
can be taken up by aquatic plants as fertilizer.Mechanical
filters physically trap and remove debris and
sediment. Sterilizing units pass water through a
tube that houses an ultraviolet bulb: The UV light kills living
microscopic particles in the water.
In my experience, a combination of biological filtration with a
proper mechanical filter (to remove solids before the water enters
the biological filtration unit) is the most effective approach.
I’ll discuss the reasons for this below.
A Simple Process
The main function of a mechanical filter is to remove debris before
it can sink to the bottom of the pond and decay. In many systems, a
skimmer unit houses the filtration medium as well as the pump and
its associated plumbing. Everything within the system is
self-contained, meaning the skimmer won’t drain the pond if a leak
develops in either the plumbing or the waterfalls.
There are two main types of skimmers: box and floating skimmers.
Both types filter the water by removing floating debris and waste
before it’s had a chance to fall to the bottom of the pond — but
the box skimmer is generally easier to maintain.
Box-style skimmers come with either vertical or horizontal filter
mats. Horizontal mats lie flat, so there’s no sagging that distorts
their shape. Also, they can’t clog to the point of preventing water
passage, so there’s no danger of the pump running dry. By
comparison, vertical mats require more frequent cleaning and need
to be monitored to make sure there’s enough water in the chamber
for safe pump operation.
With either orientation, as water enters the skimmer the large
debris is removed and the water is then further filtered through
the mats. The water then travels through its buried plumbing and
moves to the biological filter, where it’s further treated before
re-entering the pond.
Water enters the biological filter, which is typically placed on
the opposite side of the pond from the skimmer via a pipe located
near the base of the unit. The water then flows from the bottom to
the top of the device, traveling through the filtration medium
housed inside the unit. This medium helps by removing fine- to
medium-sized particles; the larger debris was removed in the
skimmer.
The biological filter fills and ultimately overflows to cascade
down rocks arranged into a naturalistic waterfall configuration.
There’s the added benefit here in that the waterfall aerates the
pond, assisting in the circulation and in the overall health of the
water. (If a slower, stream effect is preferred, the unit simply
needs to be sunk lower into the ground.)
Biological filters on the market today range in size and can filter
ponds up to 10,000 gallons. For larger ponds, multiple biological
filters can be incorporated into the design.
Background Science
Mechanical and biological filtration are critical to processing the
many types of nutrients found in a watergarden system, including
fish wastes, uneaten fish food, leaves and runoff from lawns (to
name just a few). Left to their own devices, these materials
generate high levels of ammonia, a form of nitrogen that is highly
toxic to fish and is also a major contributor to prolific algae
growth.
A biological filter does its job by virtue of the fact its
filtering medium is impregnated with nitrifying (or facultative)
bacteria that absorb ammonia and turn
its nitrites into
less-dangerous nitrates.
(These bacteria require oxygen to live, so it’s important for the
pond’s pump to run 24 hours a day, seven days a week. If the pump
stops running, the waterfall also ceases to flow and aeration is
eliminated, and the equations required to maintain the ecosystem
are thrown out of whack. In particular, once the pump shuts down,
the bacteria in the biological filter will quickly use up all of
the available oxygen and die — not a good
thing.)
Once the bacteria have done their work, the resulting nitrates are
removed from the pond by another biological filtration method known
as de-nitrification. This process occurs only in anaerobic
(oxygen-free) areas of the pond, which is why it’s not necessarily
bad for some areas of a pond to experience minimal water flow (such
as on the bottom of the pond under an inch or so of gravel). The
bacteria living in this area of the pond turn nitrates into
nitrogen gas that is released into the atmosphere or absorbed by
aquatic plants — or by algae, which is another reason why a pond
without aquatic plants will become a maintenance
nightmare.
For any biological filtration to work, you need to
put billions of bacteria to work in purifying the
water. They prefer to anchor onto things, which is why surface area
is so important, with more surface area meaning more bacteria, and
more bacteria meaning better biological filtration. This surface
area is provided by filter media, rocks and gravel. Thus, a pond
with gravel on the bottom will contain more surface area for
bacteria than will a pond with an exposed liner on the
bottom.
The simple process of repeatedly turning the water over through the
mechanical and biological filters helps maintain high-quality water
and aids in creating a naturally balanced, low-maintenance
ecosystem. Add the remaining components of fish, plants, aeration,
rock and gravel, and you’ll find greater success in creating
easy-to-maintain watergardens for your clients.
When those clients spend less time fiddling in the backyard on pond
chores, it means they will enjoy more leisure time relaxing by
their backyard oasis with a cool beverage in hand. So instead of
spending your days on follow-up maintenance and troubleshooting
calls, you can instead focus on more important things — such as
gathering new clients!
Dave Kelly is Vice President of Product
Development for Aquascape, a waterfeature design and installation
company headquartered in St. Charles, Ill. Patented products that
carry Dave's stamp include the company's constructed wetland,
pondless waterfall, and skimmers. He is also the co-author of The
Pond Builder's Bible and Pond Building for
Hobbyists
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