About Pond Algae

Learning about algae and the various algae control treatments is necessary when maintaining a water garden or Koi pond. If algae control treatments are not used, an algae bloom can turn your once beautiful pond into a living nightmare. Your pond may end up having murky green water, blankets of green muck on the water surface, or strings of algae in your streams and waterfalls.

Algae can be found in virtually any backyard garden pond. It can either be beneficial or harmful depending on the type and the excessiveness of the algae.

One of the benefits of algae is that it helps remove excess nutrients that build up in your pond water over time. This excess of nutrients can be unhealthy for plants, fish, and other aquatic life.

The downfall of algae is when control is not being used. What can happen in an uncontrolled pond is an excessive and rapid growth of algae called an algae bloom. These blooms can harm aquatic life by competing for resources as well as destroy the water quality and beauty of a backyard pond. Certain varieties of pond algae, such as blue-green algae, can even be toxic to animals and humans.

The purpose of controlling algae is not to eliminate all algae but to maintain a beneficial balance of "good" algae so that it works for your pond rather than against your pond. There are various algae control treatments and methods you can use to accomplish this. Some control methods include:

  • Barley straw
  • UV sterilizers
  • Algaecides
  • Dyes
  • Bacterial and enzyme treatments
  • Skimmers and biological filters
  • Natural methods - Plants and algae eaters

Before we discuss these treatments and methods you need to know a little more about the types of algae and the conditions for algae growth. By knowing these you stand a better chance at choosing the best treatment for controlling algae growth and blooms in your pond.

Types of Pond Algae

There are many varieties of algae that you may find in your pond. The most common types of pond algae are filamentous and planktonic.

Planktonic Algae

Green algae - green water - blue-green algae - green pea soup

Tiny microscopic single celled algae suspended a few feet below the surface of the water where sunlight is still available for photosynthesis. Garden ponds will typically have murky green water or blue-green water if this type of algae is present.

Filamentous Algae

String algae - hair algae - blanket algae

Typically referred to as pond scum, pond moss, string algae, and blanket algae. This filamentous algae bond with other filamentous algae creating strings and lime-green mats floating on the surface of a pond. You can also find it growing in pond waterfalls, shallow streams, and attached to rocks and/or the sides of ponds where sunlight is present.

Conditions For Algae Growth and Blooms

Water Nutrients

Most algae obtain nutrients from the actual pond water not "pond soil". Excessive levels of algae occur when nutrients, especially phosphorus and nitrogen, are at high levels in your pond. These nutrients are typically cause by decomposing materials left in the pond. Dead algae, plants, leaves, and also pond sludge are a few examples of these decomposing materials. Excessive nutrients can also be produced by excessive fish waste (usually caused by overstocking of fish) and uneaten fish food. Beneficial bacteria break down the ammonia in fish waste and as a byproduct phosphorus and nitrates are produced.

Sunlight

For most plant life sunlight is required for photosynthesis. Most algae must stay toward the surface of the pond, waterfalls, shallows, and streams where it can get sufficient sunlight.

Water Temperature

Usually warmer water temperatures tend to support algae growth. Many times it is hard to control the temperature of the water because it naturally fluctuates day to day and between seasons. If you have fish and aquatic plants you will have to be able maintain a certain water temperature zone. The sad news is the water temperature that is needed to support most other aquatic life usually will be in "the zone" for algae.

The foundation of algae control is to reduce the amount of algae in your garden pond by killing it or by removing one or more conditions that promote algae growth. By removing any one of the conditions you effectively reduce the amount of current pond algae, algae blooms, and also PREVENT new algae growth.

How to Control Algae in Your Pond: Treatments and Methods

Below are the most common treatments and methods for controlling algae. Keep in mind that each treatment or method can have upsides and downsides and may not work very well to control all types of algae. Worse yet, some may not work well with Koi fish, plants, or other aquatic life.

Barley Straw

Barley straw is an excellent way to inhibit the growth of algae. Barley straw is cost effective, easy to use, and does not have any known toxic effects on aquatic plants or fish. More about barley straw.

Ultraviolet Sterilizers

Ultraviolet sterilizers are very important for controlling algae and keeping your pond balanced especially if you have fish in your pond. UV sterilizers are sometimes referred to as clarifiers and are an important water treatment for killing free-floating bacteria, suspended algae (planktonic algae and green water), fungi, mold spores, viruses, and other parasites. The downside to UV sterilizers is that the algae must pass in front of the light so any attached algae will not be killed.

It is EXTREMELY important to use the right size of ultraviolet sterilizer for your pond size and water flow. Also keep in mind that all UV sterilizers are not created equal and some water UV clarifiers will only keep the water clear for the top foot or so. You should also wait a month or two before adding an ultraviolet sterilizer to a new pond.

Skimmers and Biological Filters

Skimmers - If your pond is not too large, a skimmer can help trap and filter debris from your pond water. Such debris when left in your pond will start to decompose which creates nutrients for pond algae. Although skimmers aren't the best method for controlling algae, they can provide a tiny bit of assistance. Skimmers must also be cleaned out regularly so water can pass through.

Biological filters - If you maintain a Koi pond you will probably have a biological filter. Most biological filters do nothing for controlling algae. These filters contain beneficial bacteria that break down toxic ammonia from fish waste. The reason we mention these filters is that they produce nitrates (aquatic plant food and algae food) during the process of breaking down ammonia. So you must remove the nitrates by partial water changes or by having enough plant life to consume the nitrates.

Chemical Treatments (algaecides) and Water Treatments

Algaecides - It is recommended that you avoid chemical treatments such as algaecides. Just know that algaecides may have adverse effects and may harm plants, fish, and other aquatic life. Many of them can be harmful to the environment as well. Algaecides work temporarily and when algaecides "wear off" another algae bloom (usually worse) is sure to happen.

Dyes - Dyes are water treatments that shade the water. The shading cuts off vital sunlight algae must have for photosynthesis.

Bacterial and Enzyme Water Treatments - These are probably the most popular type of water treatments and water clarifiers available. There are also a wide variety of bacterial and enzyme treatments that can control combinations of water pH, sludge, and to remove ammonia and excess nitrates. Many control algae very well and are safe for fish, aquatic plants, and the also the environment. You can also find treatments, such as GreenEx, that specifically help control filamentous algae (string algae).

Natural Controls

Plants - Adding plants to your pond is a great natural way to help control algae. Aquatic plants can control algae by consuming nutrients needed for algae growth. They can also help shade the water therefore removing the required sunlight algae need for photosynthesis. Overhanging "dry land" plants can also help to shade the water. Be sure to keep any dead foliage out of your pond as decomposing material can add nutrients to the water. 45%-70% shading is recommended if you are trying to control algae by shade alone.

Some aquatic plants to look into are the water lily, water lettuce, water hyacinth, snowflake, yellow flag iris, cattails, and duckweed. Be careful with the duckweed since it could take over your pond if you are not careful.

Algae Eating Fish - It may not hurt to have one of these guys running around in your pond. They help "clean" your pond simply by eating the algae growing on the bottom and sides of the pond. Tadpoles and snails are also help if you want an alternative.