Which of the following is a copper algicide product?

• A. Chlorine
• B. Lime
• C. Copper sulfate
• D. Alum

Answer: (C)

Copper-based algicides work by releasing copper ions into the water, and those ions are toxic to algae, disrupting photosynthesis and enzyme function to slow or stop growth. Copper sulfate is a classic example of a copper-containing algicide: when it dissolves, it provides Cu2+ ions that actively suppress algae. The other options aren’t copper-based algicides: chlorine is an oxidizing disinfectant that can affect some algae but isn’t a copper product; lime is used to raise pH and adjust hardness; alum is a coagulant that helps clarify water rather than killing algae. So the copper-containing option is the correct choice. Remember that copper availability and toxicity depend on water chemistry, so follow label directions and monitor to protect aquatic life.