Black stains in a pool are most commonly caused by black algae, a stubborn form of bacteria that forms hard, spot-like colonies resistant to standard chemical treatments. Removing these stains requires targeted treatment and persistence.
Targeting Black Stains: The Chlorine Tablet Method
One effective way to tackle persistent black algae spots, particularly on plaster or concrete surfaces, is through direct application of chlorine. This method helps penetrate the protective layer of the algae and attack the roots.
Using Chlorine Tablets for Spot Treatment
As recommended, you can use chlorine tablets for direct application:
- Break a tablet in half. This makes it easier to handle and apply directly to the specific stained area.
- Rub it directly onto the surfaces affected by black algae. Carefully hold the broken tablet and rub it firmly over each black spot. Be thorough, ensuring the tablet makes direct contact with the stain.
- This will help kill the roots and prevent it from growing back. The concentrated chlorine at the point of contact is powerful enough to destroy the algae's roots embedded in the pool surface, which is key to preventing recurrence.
Important Considerations & Safety
- This method is best suited for plaster or concrete pools. Use with caution on vinyl liners as direct contact with chlorine tablets can damage the liner.
- Always wear protective gloves and eye protection when handling chlorine tablets.
- Ensure proper pool water chemistry is maintained alongside this spot treatment for overall pool health.
Comprehensive Treatment for Black Algae
While the chlorine tablet method is excellent for targeted spot treatment, effectively eradicating black algae often requires a multi-step approach:
- Brush Rigorously: Black algae forms a tough protective layer. Before any chemical treatment, use a stiff pool brush (like a wire brush for plaster pools) to aggressively brush the affected areas. This breaks open the colonies and allows chemicals to penetrate. Brush multiple times daily if possible.
- High Pool Shock: Perform a high-dose shock treatment on your entire pool. Follow product instructions for treating black algae, which usually requires a significantly higher dose of chlorine than routine shocking.
- Apply Algaecide: Use a high-quality algaecide specifically formulated for black algae. Follow product instructions carefully.
- Maintain Filtration: Run your pool filter continuously for 24-48 hours after treatment to help clear dead algae particles. Backwash or clean your filter frequently.
- Brush Again: Continue brushing the affected areas daily even after chemical treatment to remove remnants and check for regrowth.
Preventing Recurrence
Once the black stains are gone, preventative measures are crucial:
- Regular Brushing: Even in areas where algae isn't visible, regular brushing, especially in corners and crevices, disrupts potential growth.
- Maintain Proper Water Chemistry: Keep your chlorine levels, pH, and alkalinity balanced. Test your water regularly.
- Clean Filtration System: Ensure your filter is clean and running efficiently.
By combining targeted treatments like rubbing with chlorine tablets on stubborn spots with a comprehensive approach of brushing, shocking, and proper maintenance, you can effectively remove and prevent black stains in your pool.
