String algae is a nuissance to say the least! Adding barley extract, pellets , or straw is a great proactive approach to prevent heavy string algae outbreaks. Barley should be added in the spring when you open your pond or pondless waterfall. This will give it time to break down the barley to produce the enzyme that helps get rid of string algae. If you are using the straw or pellets you will want to check on them every two months - if its really broken down it is time to add a new bag of barley straw or pellets. Leave the old bag of barley in there for about two weeks after adding the new bag. After two weeks have passed the old bag can be removed.