Best way to control FA in a small pond environment is remove it, in my opinion. Get a big landscaping rake and pull the stubborn patches out with it. Spraying or applying granular algaecide will kill the patches, but if you leave them in the pond they will release their nutrients back into the water and you'll be fighting that fight again in no time. If you do decide to go that route, Cutrine is a popular and effective algaecide.
