As long as you are only spraying small areas for killing gently breeze concentrated algae youi can keep applying the Cutrine mixture. It is best used on sunny days when the algae is primarily at the surface. Keep in mind as long as you don't have any type of submerged vegetation the natural competition and growth of submerged plants there will regularly be these green surface films to deal with. Why wouldn't there be these invasive films when nothing else green is allowed to grow in the pond?

aka Pond Doctor & Dr. Perca Read Pond Boss Magazine -
America's Journal of Pond Management