A pond skimmer is a type of
mechanical filter used in constructed ponds to remove organic matter and
other debris floating on the surface. Powered by a pond pump, the skimmer sucks
water in and through a mesh bag or plastic filter basket. Any material large
enough is caught by the basket and can be easily removed from the pond; roughly
85% of debris can be caught with a skimmer before sinking to the bottom.
A skimmer is a good idea for most
garden ponds specially if you have a lot of trees in the area. They are a
pond’s first line of defense when it comes to keeping water clear and pure.
A weir at the mouth of the skimmer restricts the depth of the water drawn into
the reservoir. Most of these weirs are positioned with floats to ensure that
the flap lowers as the water level of the pond drops. If the skimmer reservoir
ever empties completely, for any reason, then the pump will run dry and over
heat. Low water cut-off switches are essential with skimmers.
Some surface debris is too small to be collected by a pond skimmer net or
basket. The basket is sized to stop the passage of large materials while
allowing water throughput sufficient for the pump. Most skimmer boxes hold a
filter mat or brush-type filter in a slot behind the netting. These filters
catch smaller debris, such as dead insects and tree pollen, unimpeded by the
The keys to proper operation of a pond skimmer are flow and cleaning. When the
skimmer weir is working properly, it will allow only the upper inch or so of
surface water to enter the skimmer box. A shallow restriction results in a
higher velocity through the skimmer weir and a more effective draw through the
filters, but it also reduces the tolerance for fluctuation in water level. If
the water level of the pond ever drops to a point where water cannot be drawn
over the skimmer weir, then the pump will empty the skimmer reservoir and run
dry with disastrous consequences.
A pond skimmer must be cleaned periodically for the same reason. Accumulated
debris in the netting or skimmer brush filters can decrease the flow to the
reservoir. The pump may then drain the skimmer reservoir faster than incoming
water can supply it.