You need to stop the source of all the nutrients feeding the algae. Last year my FA was really bad due to all the rotting cattails and flooded over grasses around my pond. I started cleaning the FA out with just a pool skimmer and rake for about an hour the first day and for about 20 minutes after that at a time every few days. Now my 1/2 acre pond is very clean looking. I would not want to do it by hand on a much bigger pond however.