During the summer months, many pond owners are plagued by String Algae. String algae are fibrous green strands of algae (which can look like long strands of green hair), which can grow out of control if not kept in check. Excessive growth of the string algae removes the oxygen that fish need from the pond water and chokes the pond. There is a five-step process for the treatment of string algae.

Step 1.

Physically remove as much of the string algae as possible before treatment to minimize the amount of decay. Many pond owners will pull the algae out by hand, others purchase a long-handled brush and wrap the string algae around the brush to pull it out.

Step 2.

To kill off the remaining algae, use a pond algaecide safe for fish and plants. We have found a liquid algaecide to be the most effective and safe for ornamental ponds. It is best to treat your pond on a sunny day in the morning. Algaecides will pull oxygen out of the water, so we recommend you pour the treatment into a high flow water area such as a waterfall to minimize the impact on plants and fish. During the treatment phase, we recommend using the algae fix every three days until the algae turn brown. Once the algae is under control we have found using the liquid algaecide once a week can be an excellent preventative of recurring string algae.

Step 3.

Add barley to your pond to prevent and/or slow down the new growth of string algae. When barley breaks down it releases a hydrogen peroxide gas that deters the growth of string algae. Barley is available in several forms:

  • Bales (Large Bales are available for Earth/Natural Ponds) - Bales are the least expensive but take four to six weeks before they break down and begin to release the hydrogen peroxide gas. The bales can be placed in your filter (if room allows) or directly in your pond with a string attached that is tied to a rock to weight it down. The bales should be replaced every two to three months. When putting a new bale in, leave the old bale in for 6 weeks to give the new bale time to break down and start working.
  • Liquid – The liquid form of barley is the quickest acting (because the barley has already been broken down), most effective, and as you might expect, most expensive.

Step 4.

Look for potential causes of the string algae growth. High pH and Phosphorus are the leading causes. To determine if you have high pH or Phosphorus use a test kit or take a water sample to a pond, water garden, or fish store.

  • If your pH is high (above 8.5), use a pH down the product to reduce the pH. Once the pH is between 6.5 and 8.5 add a pH stabilizer to keep the pH at the new level. Also, look for the cause of the high pH and remedy it. Common causes include excessive plant growth, overstocking of fish, the introduction of foreign materials (untreated concrete, rocks containing limestone or calcium, granite), or the clearing of algae blooms. It should be noted that Green Water Algae could cause major pH swings. If you have Green Water you should solve the Green Water problem first, then adjust pH if it is still an issue. Note: Changes to pH MUST be made GRADUALLY. Do not attempt to alter the pH more than 0.2 in a 24-hour period (except with a pH crash, in this situation dramatic changes are required). Be sure to follow the instructions on the labels.
  • If Phosphorus content is high, use Phosphorus Remover (Placed in a filter media bag in the filter). A common source of high phosphorus is fertilizer. When fertilizing your lawn be sure to use a non-phosphate fertilizer.

Step 5.

Use a sludge-eating bacterium to break down the remaining organic matter resulting from the dead algae. Sludge-eating bacteria is available in two forms:

  • Liquid Form – Just Pour into Pond
  • Granular Form - Now comes in water-soluble packets. Simply toss in one packet per 1000 gallons once a week.


Pond Maintenance & Service, Pond Construction & EquipmentSeawall Construction