Use this quick test for algae problems in the pond to check how much phosphate your pond water contains. Phosphates are the main cause of excessive algae growth. If the phosphate value is above 0.1 mg/l, you can absorb the phosphates with a phosphate binder such as JBL PhosEx Pond and thus deprive the algae of their food source.
You can find more about the water test, detailed instructions for use and how to purchase it here: JBL PROAQUATEST PO4 Phosphate koi .
Find more about combating algae in the Themeworld Pond at: Combating algae .