Algae growth is a common issue in water features of all sizes, from small garden ponds up to our oceans. Fortunately, while it might seem like an insurmountable issue, if you have a pond or small lake, algae control is far easier than it is for large bodies of water, such as Lake Huron or Lake Michigan, which have seen harmful algal blooms during the last few years.

What Causes Algae Growth?

Several factors can contribute to the growth of algae, including:

  • Improper aeration
  • Improper filtration
  • Too many fish
  • Too much sludge & debris
  • Too much sunlight

In general, algae thrive in environments with compromised oxygen levels and the above-mentioned factors can cause oxygen levels to drop, creating a perfect breeding ground for algae growth. Let’s take a quick look at each of these factors.


An aeration system is an essential component for any pond, but especially for a pond stocked with fish. This circulates and oxygenates the water, and you need an aeration system that can circulate all of your pond water at least twice every 24 hours.


Fish waste and other animal waste, as well as other debris, can be removed using a filtration system and this can prevent many common pond water issues and curb algae growth.

Too Many Fish

Fish need oxygen and if there are too many fish, then these creatures must compete for oxygen. Additionally, fish produce waste and this waste settles at the bottom of your pond and contributes to the sludge layer. If you have too many fish, there’s too much waste. Oxygen levels drop and this promotes algae growth. Rehoming some of your fish so that there is adequate oxygen can be a great option for algae control.

Too Much Sludge

Fish waste can contribute to that sludge layer, but many other types of debris also can sink to the bottom of your pond and build up. When the sludge layer of your pond becomes too thick, this also causes oxygen levels to drop, and the water will contain excess nutrients that algae feed on.

Controlling your fish population can help reduce sludge, but you also need to keep debris such as dead leaves and grass out of your pond. You can create a buffer or barrier of beneficial plants around the edge of your pond to keep runoff and some debris from your pond. We also recommend using a grass catchment system on your mower as well as raking up dead leaves and ensuring these don’t enter your pond. With a small pond or koi pond, skim the pond daily to remove any floating debris. With larger ponds, you may need to hire someone to come out and dredge your lake and remove the sludge and muck.

Too Much Sunlight

If your pond has too much direct sunlight, this can cause algae growth. As a general rule of thumb, about 40% of your pond should be shaded. This can be accomplished by planting a tree or shade plants or adding floating plants to your pond, although you need to make sure that these floating plants don’t begin to grow and cover too much of the surface. Pond colorant or dye also can be added to reduce the penetration of sunlight.

Types of Algae

There are thousands of species of algae on the planet, but they won’t all be causing problems in your pond water. Typically, the algae terms you will hear in regard to your pond include filamentous algae, planktonic algae and plant-like macroalgae.

Filamentous algae are stringy or thread-like and when they reach the surface, they are commonly called pond scum. Planktonic algae are microscopic and can be pea soup green or brown. In small amounts, these can be beneficial, but when they “bloom,” planktonic algae can cause oxygen levels in your pond to drop.

Macroalgae, such as chara, is a plant-like form of algae, often mistaken for a weed. Small amounts of some macroalgae can be beneficial, but when they begin to grow out of control, this can cause oxygen levels in your pond to drop and chara can grow rapidly. Nitella is another common type of macroalgae that can grow out of control in your pond.

Ponds water also can be damaged by what is often called blue-green algae, however, this is not actually algae, but cyanobacteria. Algae and weeds can cause many pond water problems, but cyanobacteria are an especially serious problem. Cyanobacteria is dangerous for fish, but also for any livestock, pets and even humans. This requires immediate attention and remediation.

Algae Control Products

Addressing the issues that cause algae growth is the best way to prevent algae from becoming an issue in your pond. However, if you already have algae in your pond, we have some chemical pond treatment products that effectively kill algae and aquatic weeds.

For instance, Captain is a fast-acting liquid copper algaecide that can be used to control a broad spectrum of filamentous algae and planktonic algae, musk grass and more. If your pond is stocked with koi or trout, Captain cannot be used, so please contact us at (877) 948-0303 or head to our free treatment planner at

We know that algae control can be frustrating and confusing, so please do not hesitate to get in touch with us if you have any questions about our products or pond maintenance. In addition to algae and cyanobacteria, there are many invasive species of weeds that can upset the balance of your pond water, and we can match you with products that will help improve your water quality and prevent issues such as algae growth and weed growth.

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Why Choose to Autoship?
  • Automatically re-order your favorite products on your schedule.
  • Easily change the products or shipping date for your upcoming Scheduled Orders.
  • Pause or cancel any time.