A filter is the easiest way to control algae growth in the pond and to keep the pond water clear. This is especially important if there are fish in the pond. You cannot use an algaecide if there are fish. The pond water should be clean and free of harmful microbial growth for the health of the fish. While covering the pond water with floating plants will protect the water from large debris, they cannot prevent small particles from getting into the water. Also, they are not very effective at controlling algae growth. But if there are no plants or fish, you can simply do the pond with some algicide once every two weeks.