If your algae looks like cotton candy or stringy hair in water then you have filamentous algae FA. For no or minimal chemical control use tilapia with around 30-40 lbs per acre are often suggested. In light infestations of FA you can use fewer tilapia of around 20lb/ac or for heavy amounts of FA it may take 50lb/ac. It is usually best to try and reduce the amount of FA before adding the tilapia so they are not overwhelmed by too much FA to eat when you stock them. Too much and too few tilapia and lack of FA control is often the result.
For other methods of dealing with it read through and study the info in this thread from our Common Pond Q&A Archives.
http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=92633#Post92633A pond with lots of FA basically means the nutrient concentrations are out of balance and too few natural plants are present to compete with FA. Higher plants and FA compete for the same nutrients. The most abundant one thrives abundantly often to the point of nuisance.
