Help! My pond has algae!

Help! My pond has algae!

Nothing is more discouraging than to see your pristine pond water to become green soup or have your freshly cleaned pond to turn into a green hairy monster almost overnight. Presence of algae in water gardens is a normal and beneficial unless the amount goes out of control which referred as “algae blooms”.

Algae definition: a simple, nonflowering, and typically aquatic plant of a large group that includes the seaweeds and many single-celled forms. Algae contain chlorophyll but lack true stems, roots, leaves, and vascular tissue.

The two most common forms of algae in decorative ponds are: planktonic and filamentous.

  1. Planktonic algae are the floating microscopic vegetation that is making your water look like a green pea soup.
  2. Filamentous (string) algae is a string algae. It looks like long green hair attached to rocks, other aquatic plants and whatever it finds to attach to. Sometimes it gets loose and floats on top of the surface as greenish yellowish clamps, referred to as pond scum.

Algae problems occur when an overabundance of nutrients (nitrogen and phosphorus) enter the pond and may impact any pond including even the cleanest ones when conditions are “good” for algae to grow:

  • Amount of fresh water. Fresh water disturbs the natural balance of bacteria that feeds on algae, thus creating imbalance in the pond. If you need to top off water more than 1- 2 inches per week, check and repair leaks in your pond to restore balance. Add beneficial bacteria monthly to help with freshwater topping.
  • Number of fish and fish food. Fish waste creates nutrients that are beneficial to pond plants and to…. algae. Feed your fish several times a day if you want but only the amount they can eat in 5 minutes. Consider donating some of your fish or upgrade your pond to bigger one if you have more than 1-2 Koi or 2-3 goldfish per 200 gallons of water.
  • Amount of sun. Algae is a plant that requires the sun to grow. Make sure that 40-60% of your pond surface is covered by aquatic plants.

How to deal with algae.

Naturally. The way to get rid of or reduce the algae in your pond is by reducing the amount of sunlight and nutrients available to it. This process takes longer but ensures more success over the season.

  • Add aquatic plants – similar to algae, plants use nutrients that are in the pond. Covering 40-60% of your pond with plants (water lilies pads, floating plants) not only means there will be fewer nutrients available for different types of algae to use, but they will also shade your pond.
  • Improve filtration –ponds with many fish need more filtration. If you water is not clear, time to upgrade your filtration system.
  • Add aeration – it will help to add more oxygen for the fish as well as help beneficial bacteria to be more active. o Beneficial Bacteria – helps to balance your pond water by consuming extra nutrients. o Add Barley products. Barley Straws are inexpensive and safe to use in ponds with fish and other wildlife. Barley can be used during the winter months when other pond treatments are ineffective.
  • For “green pea soup” algae, adding fine mesh filter pad to skimmer to filter water for few weeks may help. Make sure to clean this filter daily.


Non-chemical treatments

  • Installing a pond UV clarifier light is a more expensive but recommended solution for ponds in full sunlight. UV clarifiers are designed to destroy the ultrafine particles in the water.
  • Ionizers: Copper ionizers for ponds are designed to release copper ions into the water to keep it clear and reduce string algae buildup. Ionizers can easily be incorporated into new or existing ponds by placing a drop-in model into your pond skimmer.


Chemically. There are many products available. Use them according to the product label. Chemical treatments will help to clear water fast, but they are a temporarily solution. Regardless of the chemical product, make sure to

  • Physically remove as much string algae as possible before treating with chemicals
  • Do not overdose as those products may harm your other plants and fish.
    • Remove dead algae daily. Dying algae will add more nutrients to the water promoting more algae blooms. Clean out skimmer’s basket every day during the treatment.
    • Have adequate filtration: do not turn off your water pump filtration and add an additional aeration for the fish as dying algae will consume more oxygen.

Let's keep your pond looking great!


Phone: (847) 226-1718

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