Black Algae: How to Get Rid of This Pool Nightmare

Of all the unsightly issues that can plague a swimming pool, nothing inspires more dread than the sight of black algae. Unlike its more common green or mustard-colored cousins, black algae is a formidable foe. It is not just an eyesore; it’s a resilient, hard-to-kill organism that can wreak havoc on your pool’s surfaces and overall health.¹

If you’re seeing small, dark spots on your pool’s plaster, concrete, or grout, you’re not dealing with a simple algae bloom. You’re facing a stubborn, microscopic plant-like organism (technically a cyanobacterium) that has an ingenious defense system. This article will provide you with a comprehensive, step-by-step guide to get rid of black algae, explain the dangers of black algae, and outline the best prevention methods to ensure it never returns.

What Makes Black Algae So Dangerous and Difficult to Remove?

First, it’s important to understand why black algae is so much worse than a typical algae infestation. The reasons are a combination of its physical structure and its resilience.

1. A Protective Outer Layer: Black algae forms a thick, waxy, protective outer coating. This “head” or “cap” shields the organism from your pool sanitizer, making it incredibly difficult for standard chlorine levels to penetrate and kill the organism.
2. Deep-Seated Roots: Unlike green algae, which floats freely or clings to surfaces, black algae develops deep, embedded “roots” that burrow into porous surfaces like plaster, concrete, gunite, and grout. Even if you scrape off the visible head, the roots remain, and the algae will simply regrow. This is why a simple shock treatment and brush won’t solve the problem.
3. Encourages Bacteria Growth: The biggest danger of black algae is not the organism itself, but what it attracts. Black algae’s presence can encourage the growth of harmful bacteria, including E. coli, which poses a serious health risk. It’s best to avoid swimming in a pool with a black algae problem until it’s completely eradicated.
4. Structural Damage: Over time, the deep-burrowing roots can cause structural damage to your pool’s finish, leading to cracks and the need for expensive resurfacing.

How to Get Rid of Black Algae: A Step-by-Step Eradication Plan

Successfully treating black algae requires a multi-pronged, aggressive approach. You can’t just throw more chlorine at it and hope for the best. Follow these steps meticulously to ensure you kill the algae at its root.

Step 1: Get the Right Tools and Prep Your Pool

Before you begin, gather your supplies. You’ll need:

• A Stainless-Steel Bristle Brush: This is non-negotiable for concrete or gunite pools. The tough bristles are required to break through the algae’s protective layer. For vinyl or fiberglass pools, a stiff nylon brush is the safest option.
• Specialty Black Algae Treatment: You’ll need an algaecide specifically formulated for black algae. Look for products containing copper or silver.
• High-Quality Pool Shock: This will be used for a super-chlorination process.
• Manual Vacuum and Pole: A manual vacuum is essential to bypass your filtration system and remove debris directly to waste.
• Safety Gear: Goggles, gloves, and old clothes are a must when handling strong chemicals.

Next, remove all toys, floats, and pool equipment from the water. Scrub them thoroughly with a bleach solution to ensure no spores are reintroduced later.

Step 2: Vigorously Scrub the Algae

This is the most critical and labor-intensive step. Vigorously scrub every single visible spot of black algae with your brush. Focus on the centers of the spots, as you must break open the protective head to allow chemicals to penetrate. Put all your weight into it and scrub until the visible spot is gone or severely diminished. Pay special attention to corners, crevices, and steps, as these are common nesting grounds.

Step 3: Super-Chlorinate Your Pool

Once you’ve broken through the protective layers, it’s time to shock the pool. For black algae, you will need a massive dose of chlorine, often triple or even quadruple the standard shock amount. A good rule of thumb is to use 3-4 pounds of calcium hypochlorite (cal-hypo) shock per 10,000 gallons of water. Always follow the product manufacturer’s instructions for the correct dosage.

Broadcast the shock directly over the areas where the algae was most prevalent. The goal is to raise the free chlorine level to a very high range (10-20 ppm) for an extended period.

Step 4: Use a Specialized Black Algae Algaecide

After you have shocked the pool, a specialty black algae algaecide is your best weapon. These algaecides are formulated with potent metallic compounds (like chelated copper) that specifically target and kill the algae’s deep-seated roots. Add the algaecide according to the product’s directions. This step is crucial because it ensures you kill the roots that survived the shock treatment, preventing the algae from returning.

Step 5: Continue to Brush and Circulate

For the next 48-72 hours, keep your pump running continuously to circulate the chemicals. Each day, take your brush and scrub the affected areas again. This helps the chemicals penetrate and kill any lingering organisms. After a few days, the black spots should be visibly gone.

Step 6: Clean Your Filter and Vacuum to Waste

Once the algae is dead, it’s time to clean up. The dead algae spores and remnants will have been caught in your pool filter. You must thoroughly clean or backwash your filter to remove any remaining spores to prevent re-contamination. Next, use a manual vacuum to vacuum any settled debris directly to waste, bypassing your filter.

For more advice on removing black Algae from the pool follow the link, Pool Black Algae – Quickest Way To Completely Kill It – YouTube

Prevention is the Best Cure: Stop Black Algae Before It Starts

Fighting black algae is a difficult and costly battle. The best strategy is to prevent it from ever taking hold.

• Maintain Perfect Water Chemistry: Black algae thrives in poorly balanced water. Consistently check and maintain your pH, alkalinity, and sanitizer levels. Keep your free chlorine consistently between 2-4 ppm.
• Brush Your Pool Weekly: Regular brushing, even when your pool looks clean, helps dislodge microscopic organisms before they can form a protective biofilm.
• Clean Your Equipment: Never use a brush, vacuum head, or pool toy in your pool that has been used in a natural body of water like a lake, river, or pond. Black algae spores can be introduced to your pool this way.
• Run Your Filter: Ensure your pool pump is running for at least 8-12 hours per day to guarantee proper circulation and filtration.
• Use a Routine Algaecide: A maintenance dose of a quality algaecide can help prevent the growth of all types of algae, including black algae.

Black algae is a tough opponent, but with the right tools, a methodical approach, and a diligent pool maintenance routine, you can win the battle and keep your swimming pool safe, clean, and beautiful for seasons to come.