If your water surface is exposed to the sun, you're going to keep
getting algae. If you cover the water surface with plants, about 75%,
that will help.

If you don't have fish in your pond, you could use stuff that puts a
film over the surface, like Aquashade. It tints the water blue and does
work to stop the growth of algae. I have used it in the past in two
small ponds I used as water gardens, no fish.

Hope this info was helpful. I am sure others here will have more
suggestions.

Denise

Visit my gardens:

http://web1.in4web.com/mtcdrc