I am a new pond owner myself. Our pond is only about 1 1/2 years old. But we had that same algea in ours last year and didnt get too bad but was a pain trying to fish. When we started seeing it come back this spring, we went to our local co-op and bought some blue dye for ponds and added to ours. It has really seemed to stop it in its tracks and made the pond a really pretty color as well....lol. Not sure but I was told that it will not kill your existing algea but will prevent new growth. Maybe check into that and especially next spring think of adding it about Feb or March to control it. Hope that helps!!! It sure helped in ours!

Happy Fishing!!!

TWilson