Recirculating and filtering water are not necessary in the “balanced” garden pond. If you do decide to move water, you will choose a pump size for one or both of two reasons:
Aesthetics - To see and/or hear a
waterfall, stream or fountain. As
a general rule of thumb, move no more than twice the
number of gallons in your pond per hour.
This tends to keep the waterfall in scale, minimizes
suspended particles, and probably leaves a quiet space for
Make your decisions in this order:
What size is the pond? How many gallons of water
does it hold? What do you want your moving water to look
like? A Bubbling rock? Waterfall? Fountain? What would be
the ideal rate of flow for the best filtration? Will
compromise be necessary? Given all that, what size pump?
Screen or mechanical filter? Hose? Bio-filter? Each decision is dependent on the
Determine the ideal flow rate:
The width (in inches) of the waterfall. For a sheer fall
over a clean edge, allow 100-200 gph per inch of sill...
less for a broken fall. This determines the "look".
Now – to select the appropriate pump, determine the following:
Head, or Rise: The vertical distance (in
feet) from the surface of the lower pond to the outlet at
the top of the waterfall or fountain.
Pressure Head: Additional pressure caused by filters, U.V. lights, etc.
Total Dynamic Head: The sum of the static head + friction head + pressure head is equal to the total dynamic head (TDH). It represents the total amount of resistance your pump is working against. With this figure and a set of pump performance charts you can determine which pump(s) will provide the desired flow rate for your project.
Other Considerations: There are usually several options for a pump in a given range. Initial purchase price, projected monthly electrical usage, length of electric cord, physical dimensions, performance, style of inlet/outlet & warranty period are all to be considered.
Mechanical Filtration: Removes particulates from the water. Usually positioned before the pump intake, e.g. skimmers & foam filter boxes, also preventing damage to the pump. The surface area and density of the materials in the filter directly affect the cleaning frequency.
Biological Filtration: Converts toxic ammonia and nitrites generated by fish waste and decaying debris to non-toxic nitrates, by passing water over filter media harboring nitrifying bacteria. The amount of biological activity taking place is directly related to the flow rate of water and the amount of surface area provided by the media.
Plant Filtration: Minimizes nitrate buildup in the pond by use of plants in the water garden and biofilter. Passing nutrient-rich water over, around and through the roots of plants causes a rapid uptake of nitrates and starves single-cell algae out of existance. Plants at the top of the biofilter help reduce pea-soup algae.
UV Sterilizers: Provide a sure cure for the green water blues! Water is pumped through a sealed chamber where harmful waterborne micro-organisms and free-floating algae are exposed to radiation emitted by a UV lamp. Proper flow rate is key to success.
Drawing courtesy of Maryland Aquatic Nurseries, Inc.
the Pump and Filter
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