Do you have a persistent reoccurring algae bloom? Do you live in Florida? If you answered yes...you most likely are experiencing a problem due to phosphates and or nitrates. Naturally occurring phosphates are the food that algae feeds on. In Florida we have Phosphate mines so in some areas the problem is worse than others. Phosphates are in just about everything from skin to fertilizers, etc... Prior to the 70's phosphates were used in laundry detergents and when it was known to cause algae blooms in our lakes and rivers.