Pond Surface Skimmers: Reduce Debris with our 4 Top Picks

Fish foods contain essential fatty acids, protein and other ingredients that cause an oily surface film, especially in heavily-fed koi ponds. Plants and algae also release natural oils that float on the surface. Pollen from flowers and trees will collect on the water too. Tree leaves, grass clippings and other plant material always seem to find their way into the pond water.

All of this organic material will create unsightly foam and murky water. Even fish slime can cause clumping of organic debris that prevents the water from looking sparkling clear.

Regular submerged and external pond filters cannot pull surface films and floating debris from the water surface.

A pond skimmer will skim off the surface layer of the water. Skimmers also act as a pre-filter, capturing floating solids before they enter the pond pump and biological filter. Skimming protects your pump from getting clogged or jammed up.

A pond skimmer keeps large particulates from gunking up your biological filter too. A skimmer reduces manual skimming with a skim net, cutting time spent on maintenance. We often get busy and don’t have time to skim the pond by hand. Eventually the debris settles to the bottom of the pond and begins to decay.

A pond skimmer works by dragging water into the skimmer box by means of a submersible water pump inside the pond.

Skimmers use a “weir” or floating door that pivots at the bottom with the top edge positioned just below water surface. The door floats so that most of the water entering the skimmer is pulled from the surface no matter what the water level is.

The incoming water is forced over the top edge, creating a high level of tension across the pond. The closer the weir edge is to the surface, the more surface tension and better skimming action. As water passes through the unit large debris is trapped in a mesh net or fine basket before it is pumped back into the pond.

Pond skimmers need to be positioned level with the water surface so the surface of the water can flow into the box. The skimmer catches large debris like leaves and collects them in its own filter basket. This prevents the debris from clogging the hose and water pump.

Some skimmers have a removable lid to hide the basket. The water pump sends water to the back into the pond or into an external pond filter for further purification.

It’s important to know how much water movement is required for your koi pond or water garden.

At a minimum, the entire volume of the pond should to be circulated at least once every 1-2 hours. Heavily stocked koi ponds typically circulate at a rate 1 - 1.5 times per hour.

For example, a 6,000-gallon pond would require 3,000 gallons per hour flow rate. The next consideration is how high the water must be pumped.

This resistance, placed on the water pump, is called head pressure. A pump’s flow rate declines as head pressure increases. High quality pumps will provide a chart showing water height vs flow rate in their specifications. For instance, a 2,000 gph pump may only pump 1,200 gph at four feet of head pressure (4 feet of lift above the water surface). Use head pressure calculations to match the pump to the required flow rate.

The size of pipe and tubing also makes a difference in the flow rate. The pipe or tubing inside diameter (ID) should be ½-inch larger than the pump outlet size. If a pump has 1 ½-inch outlet the pipe inside diameter should be 2 inches for best flow rates.

Once you know the water flow requirements you can compare skimmer specifications. Most skimmers are rated by the maximum and minimum gallons per hour of water that they can handle.

Some pond skimmers require you to cut a hole into the side of the pond (external skimmers). For smaller backyard ponds and water gardens, submersible skimmers are available.