If black algae developed in your pool liner at the end of summer and brushing chemical treatment did not seem to help should you replace liner?

Not necessarily. Black algae is a stubborn type of algae that can be difficult to remove, but it does not necessarily mean that you need to replace your pool liner. Here are a few steps you can try before considering liner replacement:

1. Shock the pool: Use a chlorine shock treatment to try to kill the black algae. Follow the instructions on the shock treatment product for proper dosage and treatment time.

2. Brush and vacuum the pool thoroughly: After shocking the pool, brush the walls and floor of the pool vigorously to loosen the dead algae. Then, vacuum the pool to remove the loosened algae. Be sure to pay extra attention to any areas where the black algae is concentrated.

3. Use an algaecide: Add an algaecide to the pool to help prevent the return of algae. Follow the instructions on the algaecide product for proper dosage and treatment time.

4. Maintain proper pool chemistry: Regularly test your pool water and adjust the pH level and chlorine levels as needed. Keeping the pool water properly balanced will help prevent the growth of algae.

5. Prevent direct sunlight: If possible, avoid exposing your pool to direct sunlight for extended periods, as this can promote algae growth. Use a pool cover or shade sail to help reduce sunlight exposure.

6. Brush the pool regularly: To prevent future algae growth, make sure to brush the pool walls and floor at least once a week. This will help remove any dirt or debris that could feed algae growth.

If you have tried all of these steps and the black algae still persists, you may need to consider replacing your pool liner. However, replacing a pool liner is a significant investment, so it's important to exhaust all other options first.