Hi Rich, Welcome to gpf. Just wondering do you have anything else like fish in the pond? Blocking the sun is a good way to cut down on algae. Also any plant that competes with it for food will help. I like floating plants because they do both at the same time. Also there are natural algae eaters like fish, tadpoles, and snails. If it is single celled algae then a uv light will kill it. I don't believe in all the chemicals and prefer to use natural things. If you have a new pond with fish its typical to have green water before it "cycles" and there is nothing you need to do but wait. People don't like the look of algae but it can provide a lot of good things for fish such as food, camouflage from predators, and a means to reduce unwanted waste like ammonia.