For controlling algae, the chemical most commonly used is 

Explanation:

• Copper Sulphate:
  • CuSO4 is the chemical formula for Copper Sulphate.
  • It is used as a fungicide, algaecide, root killer and also used as antimicrobial.
  • It is the chemical that is generally used for controlling algae.
  • Copper sulfate is used in Fehling’s and Benedict’s solutions.
• Bleaching powder:
  • The chemical formula is Ca(ClO)2
  • It is a pale yellowish powder.
  • It is used as a strong oxidizing agent in many industries.
  • It is used as a disinfectant for disinfecting water. 
• Lime:
  • It is a calcium-containing inorganic mineral.
  • It is often used in the treatment of wastewater, water softening etc.
• Alum:
  • Potassium alum is the most widely used alum.
  • Potassium alum is also used in leather tanning, used in the treatment of water as a flocculant in water purification, and also as a treatment to fireproof textiles.