What kind of algae is this? Long stringy stuff or short carpet type all over your pond sides and bottom. Or is it the free floating small particles of algae that make your water look yucky green? Leave the carpet stuff and scoop out the stringy stuff w/a clean toilet brush. If it's the fine free floating stuff a filter would get rid of that or take a plastic large basket and fill w/the white quilt batting and run a hose from a pump in the pond over the batting in bucket and let the water from the bottom of the bucket w/holes in the bottom run back into the pond. Every once in awhile when the batting clogs,gets dirty clean it off w/a hose and put back into bucket and do over and over again.