When should you add algaecide to a pool?

Adding algaecide during the initial phases of algae growth or during a shock treatment is effective because this timing maximizes its ability to prevent and control the spread of algae in the pool. Algaecides work best when applied before algae can establish a strong foothold, as they disrupt the growth and reproduction of algae cells. Additionally, if a pool is shocked—meaning an elevated level of sanitizer is used to clear up contaminants—it creates an environment that enhances the efficacy of algaecide, allowing it to work more effectively alongside the shock treatment to eliminate existing algae.

The other options do not provide the same level of effectiveness or are unnecessary. For example, adding algaecide only during winterization does not address potential algae growth during regular use or higher temperatures when algae are more likely to thrive. Similarly, applying it once a month could lead to excessive use of chemicals and may not correspond with the actual growth phases of algae. Finally, while heavy rain can introduce contaminants that spur algae growth, adding algaecide immediately after heavy rain may not be the best practice. It is more important to monitor water conditions and respond appropriately to the specific needs at that time, rather than applying algaecide based solely on precipitation.