Controlling Suspended Algae in Your Pond: How to Do It

Controlling Suspended Algae in Your Pond

Algae are present in every pond and serve important roles in the ecosystem. However, when their concentration becomes too high, it can adversely affect water quality. Suspended algae, just one type among various, are microscopic green algae that form under specific conditions and can cause water turbidity. Various methods can be employed to combat suspended algae.

What are Suspended Algae?

Suspended algae are microscopic and float in water. They are single-celled or multicellular organisms produced by green algae as plankton. In higher concentrations, suspended algae can cloud the water and form colonies. They move with the water’s flow, but some types are self-propelled. Different species of suspended algae inhabit deeper water layers during the night when it’s dark. Sunlight causes them to rise to the surface, where they undergo photosynthesis and produce oxygen. These suspended algae serve as food for water fleas and fish. The photosynthesis process leads to cell division and algae reproduction. When their numbers become excessive, water quality suffers. The algae create a visible film on the water’s surface. As these algae move vertically through the water, they can settle at the bottom, contributing to the formation of sludge and depleting the water of oxygen.

Causes of Suspended Algae

To effectively combat suspended algae in your garden pond, it’s essential to understand the causes of their formation. The presence of suspended algae doesn’t necessarily indicate an ecological imbalance in the pond; various factors can contribute to suspended algae formation:

  • Elevated phosphate levels exceeding 0.0035 milligrams per liter.
  • Increased sunlight and rising water temperatures in spring and summer.
  • Dead algae sinking to the pond’s bottom, providing the basis for new algal blooms.
  • High pH levels above 8.2 that promote algae growth.
  • Nutrient inflow through rainfall.
  • Increased nutrient content due to uneaten fish food.

Why You Should Control Suspended Algae

When the concentration of suspended algae is too high, it causes water turbidity and depletes the water of oxygen. In low concentrations, suspended algae can be beneficial as they improve water quality. They absorb nutrients and supply oxygen. They can convert roughly three times more carbon dioxide into oxygen than common plants. Suspended algae are active at night and consume just as much oxygen as they produce during the day. A significant fluctuation in oxygen levels between day and night can pose a serious threat to fish and aquatic plants when oxygen levels drop.

High concentrations of suspended algae can create a vicious cycle, adversely affecting your pond water and the fish living in it. They raise the water’s pH and reduce carbonate hardness, providing favorable conditions for new algae formation. They settle on the bottom and accelerate decomposition in the pond water, progressively worsening water quality.

How to Remove Suspended Algae – Various Methods

Algal blooms and a rapid deterioration of water quality can occur, especially during summer. A green veil forms on the water’s surface, and in severe cases, the water can “flip,” potentially leading to fish fatalities. To prevent this, it’s crucial to take action against suspended algae. Several methods can help. To prevent suspended algae from proliferating, it’s important to monitor water quality daily during the summer and take appropriate measures to improve it when necessary.

Mechanical Algae Removal

The immediate remedy to remove algae is through mechanical means. Use a fine-meshed net and proceed cautiously to avoid agitating the algae. In summer, you should remove debris from the water’s surface daily, including pollen, leaves, and insects. You can simplify this task by using a skimmer that removes algae and other impurities from the water’s surface. However, a skimmer alone may not suffice for eliminating suspended algae.

Use of Flocculants

One method for getting rid of suspended algae is by adding a flocculant to the pond. The algae will clump together and sink to the bottom, where you can easily vacuum them up with a pond sludge vacuum.

Application of a Phosphate Binder

Algae feed on phosphate, so elevated phosphate levels can promote algae growth. To combat suspended algae, you can use a phosphate binder. Various pond care products can bind or convert phosphates. There are different types of phosphate binders that you can add directly to the pond water or place in the filter. Phosphate binders starve the algae, but they do not address the root cause.

Use of Algaecides

Several types of algaecides can be used as an immediate measure against algae, but they don’t provide a long-term solution. They address the symptoms, not the root cause of suspended algae. Be cautious when using algaecides, as they can harm fish and plants in the pond. Algaecides should be used sparingly, only when accurately dosed, and with knowledge of your pond’s volume. Algaecides can be added to the filter, causing the algae to clump together.

Note: Before using algaecides, ensure that your water quality falls within the standard parameters. Algaecides are ineffective if the water quality is within the norm.

Use of a UVC Pond Clarifier

To remove suspended algae, you can employ a UVC pond clarifier. The UVC lamp must be replaced each season and works in conjunction with the pond filter and pump. The pump circulates water through the UVC clarifier, and then the water enters the filter. Ultraviolet light destroys the genetic information of the algae, causing them to clump together. The remnants are transported away by the filter. A UVC clarifier is safe for fish and plants in the pond.

Ensure Water Movement

Proper water movement can help prevent suspended algae formation in your pond. Water channels, waterfalls, or fountains can increase water movement and counteract algae growth. A pond pump is also effective in circulating the water.

Aquatic Plants as a Biological Filter

Aquatic plants act as a natural filter and can combat suspended algae. Water plants compete with algae for nutrients. Covering approximately one-third of the water surface with aquatic plants is advisable. Plants like elodea, hornwort, water milfoil, frogbit, water chestnut, and duckweed are suitable. Regularly remove dead plant parts, especially during the summer months, as they promote algae growth.

Fish as Natural Predators

One effective method to combat suspended algae is to introduce fish to your garden pond. Fish are natural predators and help maintain a biological balance. Ensure the number of fish corresponds to your pond’s size, as an excessive fish population can promote algae growth through fish waste. Goldfish or roach are suitable for smaller ponds, while larger ponds can accommodate grass carp. Water fleas, ramshorn snails, and freshwater shrimp are also effective algae eaters.

Preventing Suspended Algae Formation

The best approach is to prevent suspended algae formation. Regularly maintain your pond and use various methods to counteract algae growth:

  • Shade the pond, especially during midday.
  • Monitor water parameters daily during the summer and take corrective measures if water quality deteriorates.
  • Ensure a properly functioning capillary barrier.
  • Regularly remove impurities with a net.

When constructing a new garden pond, consider the location carefully. The pond should not be fully exposed to sunlight. To combat suspended algae formation, you can also build a stream.


In low concentrations, suspended algae can be beneficial for your pond, as they produce oxygen. However, during the night, they consume oxygen, leading to significant fluctuations in oxygen levels. In high concentrations, suspended algae cause water turbidity and can rapidly deteriorate water quality. You can counter suspended algae with a UVC pond clarifier, a pond pump, water movement, aquatic plants, and fish as natural predators.

Florian Egert

I am Florian Egert, the owner of I live with my wife and two children in Germany in a small village in the countryside.

Recent Posts