If algae form on any of yours best rain barrels system, you should remove it either using algae chemical or high-pressure water. However, the sound way to handle it would be to prevent its growth. A combination of light and heat favors the growth of algae; therefore, having the lid closed tightly helps prevent the growth of algae since the environment doesn’t endorse it. The best way to avoid algae growth is by placing it in the shade while tightly closed.