Filtration – More is Better!

The creek on the right
is excellent filtration.

FILTRATION
There are three main types of filtration that can be used singly or in combination to maintain water clarity and a healthy chemical balance in your pond. Mechanical filtration removes plant debris and leaves from the surface, biological filtration “cleans up” decaying matter, and U.V. filtration can help control algae and insect larvae. The amount of filtration needed is directly related to the fish load – more fish = more filtration needed. Let’s look at some of the options:


Mechanical
The goal here is to remove leaves, spent blooms, uneaten food and other physical matter from the pond to help reduce the amount of decaying material (more on why under “Biological”). Mechanical filtration usually consists of a skimmer with a net or mesh box to capture large items, and a second layer of filter mats that will catch smaller particles before they enter the pump. There are commercial skimmer boxes and filtration systems available, or you can build your own with plans published elsewhere. Whatever method you choose, it is important to keep mechanical filters clean, so that plant material does not begin to decay. Note: If you have a lot of deciduous trees, your system probably won’t be able to keep up with the leaves in the fall, and you will need to fish the leaves out of the pond with a net. If your pond is smaller, you can place netting over the entire surface for a few weeks, until the trees are bare.

Biological
As fish waste, uneaten food and plant material decay, they release ammonia into the water, which is very unhealthy for fish. Bacteria that grow on various surfaces within the pond will convert this ammonia into less toxic forms.  Plants growing inside the pond or in a bog will absorb and process those compounds, along with carbon dioxide released by the fish, during photosynthesis. Plants then emit oxygen back into the water. Biological filtration occurs naturally in the pond, and you can help it along by adding additional items for bacteria to grow on. A stream full of small to medium sized rocks, a bog filled with gravel, a box filled with bio-balls, or a flushable bead filter are all great media for bacteria.

U.V.
Ultraviolet (U.V.) lights can be used to supplement mechanical and biological filtration to reduce the green water caused by algae. U.V. filters are placed outside of the pond, usually after your primary biological filter, and a percentage of the water is passed through the unit. Algae plants are too small to be trapped by most filter media, so the U.V. is used to change the cellular structure of the algae, causing it to clump together. The larger clumps are then caught by the filters and removed mechanically or broken down biologically. A well-balanced pond may only need U.V. for a short period during the spring, when minimal plant cover and increased fish waste can cause an algae bloom. For optimal performance, U.V. lamps should be replaced yearly (or bi-annually if only used occasionally).

Setup and Maintenance
Filtration is one area you absolutely should not skimp on when building your pond – it’s one time when more is better. As you research filtration you will find a wide variety of commercial and homemade systems that will all be effective – for a while. In our experience, the more complicated the system, the more “fussing” it will require to set it up, and especially to clean it. It’s a good idea to ask yourself how much time you’re willing to spend, and how much fish poo you’re willing to expose yourself to. Bead filters with a back-flush system are easy to clean and provide both mechanical and biological filtration. A bog adjacent to the pond, filled with plants and gravel, is a fantastic filtration system that usually needs cleaning only once a year. If you don’t have time or the inclination for filter cleaning, many local pond installers will offer scheduled maintenance service. Whatever methods you use, it will take a while for your new pond to balance itself. Plants should be present from the beginning, and you can buy bacteria in a bottle to help kick start the bacteria cycle. Ideally, fish will be added a few at a time so as not to overload the young system with waste. It’s a good idea to test your water frequently during the first few weeks to keep track of the levels of toxins.

Ask us about a maintenance schedule for your pond (Western WA only)