Which of the following substances is commonly used to control the growth of algae and protozoa in water?

The addition of copper sulfate is widely recognized as an effective method for controlling the growth of algae and protozoa in bodies of water. Copper sulfate works by releasing copper ions, which can be toxic to various algae and protozoa species. This substance disrupts their metabolism and growth, helping to manage overgrowth that can lead to issues such as decreased water quality, unpleasant odors, and harm to aquatic life.

The other methods listed do not directly target the growth of algae and protozoa. Aeration of water can improve oxygen levels and enhance water quality, which may benefit some aquatic organisms but does not specifically control algae or protozoa populations. The addition of nitrates can inadvertently promote the growth of algae, as they are nutrients that some algae species utilize for photosynthesis. Filtration can help remove particulate matter from water but may not effectively eliminate algae or protozoa that are in suspension or attached to surfaces.