It's hard to keep skimmers off of the "must have" list of equipment for a quality pond. They work to remove floating debris from the pond while pre filtering to prevent the pump from clogging. Many units also add some filtering material. We utilize skimmers to feed bead filters and then jets - because you can run skimmers at a very high flow rate
Remember that skimmers don't always play nice with floating plants
What is a skimmer ?
Most people are familiar with skimmers from their use in swimming pools. Properly functioning skimmers will remove floating debris [allochthonous materials] from the ponds surface. Aesthetically this is desirable as it is functional - a skimmer reduces the bio load on the system and lightens the load on the bottom drain(s). Skimming action is fueled by a pump located in the skimmer unit. The influx of water traps debris in a plastic basket or net bag for easy removal. A skimmer is a key component to a well designed system. Although some purport it is all you need, it will not ultimately keep the bottom of your pond clean and not maximize re circulation
Types of Skimmers
There are 3 main types of skimmers
each with their advantages and disadvantages. Your pond setup and goals will determine which is the best unit to utilize
The most common type of skimmer is the standard box skimmer. It is dug in along side the pond and the liner is brought up along the face. It is sealed into place and needs to be set at the right height for proper skimmer function. Too low, the pump may starve for water. Too high, larger debris may not be able to enter the skimmer or you could even have an overflow. There is generally a fairly wide tolerance here however - about 1-2 inches
These skimmers are costly and take some time to install. They do have a large capacity however, and this type of design is most prevalent in the ponds we see. It is advisable to invest in a stronger unit which will survive the rigors of freezing and thawing. Thinner square units can become deformed after a few seasons
Another type of skimmer is a no-niche skimmer. These are easy to hide [under a bridge for example] and much smaller then box skimmers. They also offer self adjustment
with the water level [up to 6 inches] to ensure continual skimming action even if the
water fluctuates a few inches. On the negative side, they are harder to set up for the novice and offer limited debris capacity
I have one on my pond and it is suitable because I don't get a lot of surface debris. These units attach to 1.5 inch pipe at the bottom - this runs through the liner to a vortex or a dedicated pump in order to operate the unit. In order to function properly, a draw of at least 800 gallons per hour is required
The last type of skimmer is one that is placed right in the pond. This unit works well and is the simplest to install
as it just sits on a flat section of the pond floor and is anchored with a rock. These units have adjustable operational depth of approximately 14" to 28"
and are then self adjusting to varying water depths with the floating basket. That is the main advantage that both in-pond and the no-niche style skimmers have over a box skimmer - their tolerance of operation is 6+ inches while a box skimmers is usually less than 3"
In-pond skimmers have a decent capacity and are a good choice for those who have an existing pond
in which they want to quickly and easily add a skimmer. It is best to purchase a unit that has an external pump which is easy to replace [some units have a built in pump]. Aesthetically they can be obtrusive and their capacity is limited compared to a box skimmer