What are the chemicals added to cooling water to control algae and fouling called?

The chemicals that are specifically added to cooling water systems to control algae and fouling are typically referred to as algaecides. Algaecides are formulated to inhibit the growth of algae, which can thrive in aquatic environments, especially in the presence of sunlight and nutrients. This is crucial in industrial cooling systems, as uncontrolled algae growth can lead to fouling, which reduces the efficiency of heat exchange and can ultimately damage the system.

Though "biocides" could also be applicable in a broader sense, as biocides encompass a wider range of chemicals that can kill or inhibit the growth of various microorganisms, including bacteria and algae, algaecides are specifically targeted towards algae.

"Chemical treatment" is a general term and does not specify the purpose or type of chemicals being added to the water. "Cooling aids" is also not specific and does not capture the function of controlling biological growth in the system. Thus, the most precise term for the chemicals aimed at controlling algae growth in cooling water systems is algaecides.