Introduction to Pond Fish
Setting up the pond
Pumps and filters
Garden ponds are often stocked with many more fish than would be found in a natural pond and so benefit from the addition of a filtration system to improve water quality. This is especially true for koi ponds, where crystal-clear water is desirable to give the best view of the colors and patterns of the fish. Filtration systems are driven by electric pumps, which can also be used to create fountains and water features.
Pond pumps fall into two main categories: submersible units that function underwater, and powerful surface pumps for use only in a dry location. Submersible pumps are generally smaller and often run on a low voltage so are most suitable for smaller ponds, while external pumps for larger ponds and extensive water features usually run off household electricity. To work effectively, a pump must have sufficient capacity to cycle all of the water in the pond in two hours, so calculate the volume of water in the pond before choosing a pump. Preformed pond units often have their volume marked on the base; alternatively, when filling the pond, measure the volume by attaching a flow meter to the hose.
The choice of pump also depends on its intended function. For example, when operating a fountain, the water needs to be pumped under high pressure but at a low output, whereas for the operation of a waterfall—where the water needs to be pumped uphill—a high output from the pump is required. Refer to the manufacturer’s instructions and get advice from reputable retailers to be sure that the pump you choose is suitable for your intended use.
Maintaining water quality
Most filtration systems use separate pumps to draw water from the pond and through the filter, although pumps with an integral filter are also available. There are two main types of pond filter: internal units, which sit underwater in the pond, and external filters, which are sited outside the pond. All filtration systems function in a similar manner (see box, opposite), but the filtration media they house varies. When installing an internal filter, locate the pump as close as possible to the filter unit, to maintain the flow rate. By contrast, if the system uses an external filter chamber, locate the pump as far as possible from the filter outflow, to ensure that clean water is not simply pumped straight back through the system.
Ultraviolet systems, located between the pump and filter, are a further refinement that can be used to achieve very high water quality. Ultraviolet radiation emitted by the unit causes algae in suspension to form into clumps, which are then easily strained out of solution by the filter.
If you need to run an electrical supply from the house to the pond, hire a professional electrician, who will install cables in accordance with local building safety codes. Devices running directly off the main supply must always be connected via a ground-fault circuit interrupter (GFI). Low-voltage pumps, suitable for small ponds, do not present a hazard and need not be installed by an electrician.
POND FILTRATION EQUIPMENT
The pump is a critical component of a filtration system, providing the power to force the water through the filter unit. All designs of pumps, from submersible units to more powerful surface models, work on a similar principle: an electric motor draws water through the unit and expels it through an outlet. Most pumps are equipped with a pre-filter—ranging from sieve-type fixtures to foam-sponge attachments—which helps to prevent debris in the pond from entering the pump unit and causing a blockage.
Pond filtration systems work on the same principles as aquarium filters, albeit on a much larger scale. Water from the pond is passed through an internal or external filter unit that contains layers of filtration media. These can include brushes or layers of filter foam of different grades that sieve particulate matter from the water and also serve as biological filtration media, on which beneficial bacteria can grow. The bacteria break down ammonia produced by the fish, as well as other waste matter. Having passed through the media, the clean water then returns to the pond via the outflow or can be run through a further series of filters to maximize the water quality.
Check the filter flow rate and water quality regularly; any drop suggests that the filter needs cleaning. When cleaning a pond filter, always wash the media in dechlorinated or pond water, to safeguard the bacterial population. In a new pond, it will take time for beneficial bacteria to develop in the filter. To make sure ammonia does not build up to dangerous levels, add zeolite—a compound that removes ammonia from water—to the filter.
- Submersible pumps are designed to operate underwater and will not function outside the pond. An electric motor within the pump unit drives an impeller, which forces water out of the pump through the outlet. This creates a flow through the unit that draws water into the pump. The outlet can be connected to a pipe that leads to a filtration system or can supply a fountain or a waterfall.
- The main chamber of an external filter unit is housed outside the pond. Water is pumped in at the top, where it is delivered, as a fine spray, onto the filtration media. It first passes down through a number of foam layers— from coarse to fine—where particulate matter is trapped, and then through a layer of biological media, before being returned to the pond.
- A typical pond setup uses a submersible pump to supply an external filter by the waterside. Pumps that are used for passing water through a filtration system should be robust enough not to become choked by debris from the pond. If sufficiently powerful, a pump can be employed to operate a waterfall or fountain in addition to supplying the filtration system.