How to Maintain a Crystal Clear Pond
Author: Aqua Gardening
Date: 11 October 2022

How to Maintain a Crystal Clear Pond

Pond water turns green mainly due to the presence of algae. One can easily maintain a crystal clear pond with some preventive measures and applying treatments.

Many people believe that pond water will always be green, but this is merely a belief. Anyone can make their pond water crystal clear. To maintain a crystal clear pond, you must learn what makes the water colour green and which factors are responsible for this. Green pond water indicates the presence of microscopic algae, which are single-celled photosynthetic organisms.

Green pond water indicates the presence of microscopic algae, which are single-celled photosynthetic organisms.

  • Light green water is not a sign of bad water quality.
  • Dark green water is a real menace as it ruins the pond by killing other aquatic organisms and changing water chemistry.

When people provide excess fish food to the ponds or fertilisers enter the ponds by runoff, an algal bloom takes place and turns the pond water green. As time passes, the single-celled algae reproduce and increase the number, and finally, the water colour becomes green. However, before the water turns green, it will become cloudy.

Causes of green pond water


Different types of algae are responsible for turning the water colour green. Single-cell algae, string algae, and cyanobacteria are the most common types. Single-cell bacteria don't usually hurt the fish. String algae are filamentous and slimy. You can even pick these organisms with your hands, and unlike single-cell algae, string algae float on the water's surface. Although these algae are considered beneficial, you should keep them at bay. Cyanobacteria or blue-green algae are harmful algae. These bacteria can produce their foods through photosynthesis. Certain species of these bacteria produce cyanotoxins that are deadly for fish.


Sludge and muck are other culprits that can ruin the pond water. Although cloudy water is common after building the pond, dumping different materials or sludge can lead to an algal bloom. Tannins or other chemicals also change the water colour, and in severe cases, they can also kill the fish.

Debris and organic matter

The presence of debris and organic matter ruins the pond's water colour by turning it brown (Leaves and branches are the most common types). These natural compounds contain carbon which provides energy to micro-organisms. When these microbes start decomposing the organic matter, they use up the dissolved oxygen in the pond and damage the water quality.

Preventative ways to maintain crystal clear pond


Choose the right type of pond filteration system for the size of your pond and quantity of fish. A biofilter and UV light combined with a skimmer is a good start. To maintain crystal clear water you can add an aeration system and plant lots of aquatic plants.


Positioning is important for controlling algal growth. Direct sunlight will facilitate the photosynthesis of algae. As a result, they will quickly overgrow. Therefore you should choose a shady area or add some aquatic plants like water lilies or other objects that can shade the water's surface.

Beneficial bacteria

Applying beneficial bacteria can be a great way to control algal bloom. We have a wide range of beneficial bacteria that can be found in the water treatment category. If you decide to apply these bacteria, we recommend you avoid using tap water to clean your filter. Tap water contains chloride and fluoride ions which can kill the micro-organisms, so it is better to utilise the pond water.

Algae eaters

Add fish that eat algae. Catfish, Koi, Grass carp, and Shrimp are the best algae eaters.

Fish feeding

Don't overfeed your fish. Fish food contains a high amount of nutrients, mainly nitrate and phosphate. These two ions are responsible for algal blooms in freshwater. Always use the proper fish feed ratio.

Pond vacuum

Cleaning the pond water regularly using a pond vacuum is a great way to remove debris and other organic materials.

Water testing

Sometimes, algae growth becomes uncontrollable when the water has an imbalanced proportion of chemical compounds. For instance, when nitrate and phosphate concentration increases, the risk of algal bloom increases as well. Hence, we recommend using water testing kits to test the water chemistry to maintain its quality.

Treatments to maintain crystal clear pond water

Algal treatments

There are a wide range of products to prevent algal blooms. We have both Algae treatment powders and liquids in stock. You can use these products to fix algal blooms and also prevent them from happening.

Sludge treatments

Sludge can be treated using beneficial bacteria. This will help to decompose the sludge and waste materials without degrading the quality of the water body.

Pond vacuums

Pond vacuums are excellent for removing pond debris and keeping ponds clean. Having your own pond vacuum will save you a lot of money over the long run, compared with paying someone to come in a clean your pond.

Pond skimmers

Installing a pond skimmer can help you to remove floating debris quickly. These mechanical filters skim off the leaves and other floating materials before they sink to the bottom of the pond.

Special tip

Use our online pond volume calculator to calculate the volume of your pond. This will help you to determine the application rate for different pond treatment products, including algal treatment powder and liquid solutions.


Further reading