The Dreaded GREEN!
Whether it's hair algae on the surface of the rocks in your pond, or discolored green water ("pea soup"), it's all an eyesore! Algae is the result of a combination of factors: warmer seasonal temperatures, excessive nutrients in the water column, and the leaching of springtime fertilizers. Overfeeding is often one of the main causes of excessive nutrient buildup in the water. Uneaten food breaks down and adds to these levels. Make sure to remove all uneaten food from the pond. Feeding once daily is more than enough for the fish . They will also feed on some of the natural algae and insects within the pond.
Adding a variety of pond plants will help starve the algae. Believe it or not, it is recommended that about 60-70% of the pond surface is covered with pond plants. Plants help absorb some of the excess nutrients from the water column. Hornwort, water lettuce, and water hyacinths all make great additions to your pond or outdoor water feature. They have large root systems which allow them to easily soak up the nutrients.
You'll also want to use a pond skimming net to physically remove as much of the clumped up algae as possible - when doing this you will want to dose the pond with some SAB stream and pond clean (Ecoblast algaecide can be used in extreme conditions, but it is the most chemical-like product we have on our shelves). Using the SAB will help kill off the spores that are released into the water when the algae is broken apart.
Adding barley straw, pellets, or extract will also help break down the algae. Once the barley has fermented, the enzymes produced by the barley help rid the pond of these excess nutrients. We also highly recommend adding beneficial bacteria which also help aid in this process. It is important to follow the directions carefully on these products in order to get the desired results (a clear pond!).
If all else fails you may want to look into getting either the Iongen system (kills string algae by releasing small amounts of copper,zinc, and alluminum that "attack" the algae), or an ultraviolet sterilizer (the water passes through the ultaviolet unit, and is exposed to UV light which rids the pond of green water, parasites, protozoa, and other disease causing bacteria).