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Pond Algae Control

Pond Algae

One of the biggest problems to do with garden ponds is the growth of algae. It is an unattractive substance that causes the water to look filthy and sometimes green. It can grow as a form of scum on the surface of pond water. Algae are a collection of microscopic plants containing chlorophyll that live floating on stagnant water. They look slimy and can ruin the look and feel of your pond eventually causing damage to aquatic wildlife. The most common types of algae that infect ponds are free-floating and suspended ones like string algae and the infamous plankton algae.

Causes of pond algae

  • Hot and humid weather and exposure to too much direct sunlight

  • Stagnant water with no pond filters

  • Rotting leaves and other debris contained in the pond

  • Excessive levels of phosphate and nitrate in the pond and a higher pH level in the pond due to the use of marble, limestone or concrete

  • Insufficient healthy aquatic plants which can absorb nutrients from the pond

  • Fish waste (too many fish), over feeding fish, lawn fertilizers and decomposed fish.

  • Weather and temperature changes.

  • Low oxygen content in water.


How to control pond algae

Controlling light

  • The pond should be constructed in a location where the amount of direct sunlight will not be a problem.

  • Make sure to not locate your pond directly under a tree. Falling leaves and dripping sap can create havoc to the water quality of your pond and can even be toxic in some instances.

  • Use of floating plants and other surface dwelling plants are a great way to minimize the amount of light that penetrates the surface of the water.

Nutrient control

  • Minimize rain water penetration into pond. Rainwater carries air pollutants and particulates into the pond which can, in turn, increase the amount of nutrients in the pond water.

  • Avoid excessive feeding of fish food. Food that is eaten by your fish is digested and excreted. The excretion is a byproduct of the fish food and a source of nutrients for plants and algae.

  • Remove Rotten leaves and other debris contained in the pond

  • Avoid excessive application of water plant fertilizers.

  • Balance the pH to between 7.0 and 8.0 (always measure pH in the morning)


Filtration and UV control


  • Pond Filters are generally required to keep a Garden Pond or Water Garden healthy and clear.

  • Effective Pond Filters combine mechanical and biological Pond filtration. Biological Pond filtration involves beneficial bacteria to break down fish waste and other organic matter. Mechanical Pond filtration traps particles in some type of filter media for later removal during cleaning. Good Pond Filters accomplish both and can be fitted with Ultra Violet Clarifiers for algae control.

  • The Pond Filter must be sized correctly to insure effective cleaning and purification of the water. A Garden Pond that receives full sun needs a high volume Pond Filter

Types of pond filters

Submersible pond Filters

Submersible Pond Filters are commonly used on small ponds and water features. These types of filters sit on the bottom of the pond and filter the water internally. Water is drawn through submersible pond filters by a submersible pump, which can be attached to the filter either internally or externally, and than discharged into the pond.Pond filtration generally takes place through a replaceable mechanical filter pad and a permanent biological filter. These filters must be removed from the pond for maintenance and cleaning.

Pond filters – External gravity

In external gravity pond filters water is pumped from the pond or water feature into the filter, and than flows back into the pond by gravity. These filters must sit above the water level of the pond and are usually placed at the pond's edge. External gravity pond filters typically have a reusable/replaceable filter pad for mechanical filtration and permanent biological filter media. These pond filters are easily maintained and installed, and due to increased capacity for filter media, are generally more efficient and can handle larger debris loads than submersible pond filters. Some external gravity pond filters also incorporate ultraviolet (UV) sterilizers for further pond water clarification and algae removal.

Pond filters – External pressurized

External pressurized pond filters allow the greatest flexibility in locating your pond filter. Unlike other pond filters, these filters can be placed further away from your pond or can even be buried to hide them into your landscape. Basic pressurized pond filters consist of a sealed canister that is fed pond water through tubing from a pump. The water is then forced through a mechanical and biological filter media, than exits the filter and is returned to the pond. Some external pressurized pond filters also incorporate the use of ultraviolet (UV) sterilizers into their design to further clarify and eliminate algae from your pond's water. External pressurized pond filters can be used on both flexible liner and hard pre-form type ponds. A separate pond pump is required for operation.


Chemical control of algae

Chemically treating your pond with algaecides can help you effectively put an end to algae growth. The downside is the negative effect that algaecides can have on aquatic life. If you are planning to make use of algaecides, then you should ensure that your pond has proper filtration systems in place that can remove dead algae. In addition make sure your pond does not have aquatic plants and wildlife, as they can be severely affected by algaecides. Make sure to read instructions properly and buy only those algaecides that are approved.

An Integrated algae Management Approach:

1) Proper construction, filtration and water circulation.
2) Minimizing nutrient availability by under-feeding, preventing run-off and excess fertilizer from getting into the water.
3) Using your test kit to measure nitrates and keep them at an acceptably low level through desirable plant growth and water changes.
4) Using shading as necessary to cut down light and heating.
5) Manually removing algae and nutrients through vacuuming, netting and filter backwashing.
6) If necessary, use chemical control methods with care.


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