Getting rid of black spots on your pool patio starts with knowing what is causing them. In most cases, those dark spots are algae, mold, or mildew feeding on the moisture and organic material that collect on your pool deck. The fastest and most effective way to remove them is with a professional pressure washing or soft washing treatment that kills the growth at the root and restores the surface to its original color.

If you have noticed dark patches spreading across your concrete, pavers, or travertine pool deck, you are not alone. Pool patios in Jacksonville deal with this problem year-round because of the heat, humidity, and constant exposure to water. Here is what causes those black spots, how to remove them, and how to keep them from coming back.

What Causes Black Spots on a Pool Patio?

Several types of organic growth can cause dark stains on pool deck surfaces. Knowing which one you are dealing with helps determine the right cleaning approach.

• Black algae. This is one of the most common causes. Black algae grow in mats or patches on concrete, pavers, and natural stone. They thrive in areas that stay wet and get plenty of sunlight. Unlike green algae, black algae develop deep roots that embed into porous surfaces, making them harder to remove with scrubbing alone.
• Mold. Mold appears as dark black or brown spots and grows wherever moisture and an organic food source exist. Concrete pool decks are especially prone because the porous surface traps moisture for long periods. According to the CDC, mold exposure can cause respiratory issues for sensitive individuals, making removal important for your family’s health.
• Mildew. Mildew looks similar to mold but tends to sit flatter on the surface. It often appears as a powdery or film-like layer. Mildew grows quickly in shaded, damp areas around pool decks and is usually easier to clean than deep-rooted mold or algae.
• Lichen. Lichen looks like crusty, leaf-like patches with defined borders. It forms when algae and fungus grow together on a surface. Lichen grips tightly to concrete and stone and can be very stubborn to remove without professional treatment.

In many cases, you may have more than one type of growth on your pool patio at the same time. The warm, wet conditions around a pool create the perfect environment for all of these organisms to thrive.

Why Black Spots Spread Fast on Pool Patios in Jacksonville

Jacksonville’s climate is one of the biggest reasons pool patios develop black spots so quickly. Several factors work together to accelerate the growth:

• High humidity. Jacksonville averages 70% humidity or higher for most of the year. That constant moisture keeps your pool deck damp and gives algae and mold the water they need to grow.
• Warm temperatures. Heat speeds up biological growth. With average highs above 80 degrees for nearly half the year, your pool patio stays in the ideal temperature range for algae and mold to multiply.
• Constant water exposure. Splash water, pool overflow, rain, and sprinkler runoff keep your deck wet far more than other outdoor surfaces. That ongoing moisture creates a breeding ground for dark growth.
• Shade from screen enclosures and landscaping. Many Jacksonville pool patios sit under screen enclosures or near trees and shrubs that block direct sunlight. Shade traps moisture and prevents the surface from drying out between rains.
• Porous surfaces. Concrete, pavers, and natural stone all have tiny pores that absorb and hold water. Those pores also give algae and mold roots a place to anchor and grow below the surface.

Because of these conditions, a pool patio that looks clean today can develop visible black spots within just a few weeks during the warmer months.

How to Remove Black Spots From Your Pool Patio

There are several approaches to removing black spots from a pool deck, ranging from DIY methods to professional cleaning. The right option depends on the severity of the growth, the type of surface, and how quickly you want results.

DIY Cleaning for Minor Black Spots

For small patches of surface-level mildew or light algae, you can try cleaning the area yourself. Here is a basic approach:

1. Let the surface dry completely before you start. Algae spores spread more easily when wet.
2. Scrub the black spots with a stiff bristle broom or brush to break up the surface layer.
3. Apply a cleaning solution. A mix of one part household bleach to ten parts water works on most concrete and paver surfaces. Let it sit for 10 to 15 minutes.
4. Scrub again and rinse thoroughly with a garden hose.
5. Allow the surface to dry fully before using the pool deck.

This method can help with minor surface stains. However, it will not reach the roots of deep algae or mold that have embedded into the pores of the material. If the black spots return within a few weeks, you need a stronger approach.

Professional Pressure Washing for Black Spots on a Pool Patio

For stubborn or widespread black spots, professional pressure washing delivers the best results. A professional pressure washing service uses commercial-grade equipment and cleaning solutions to remove growth that DIY methods cannot reach.

Here is what the process typically looks like:

1. Apply a biocide cleaning solution. The technician sprays a bleach-based or biocide solution onto the entire pool deck. This solution soaks into the pores of the surface and kills algae, mold, and mildew at the root level.
2. Allow dwell time. The solution needs 10 to 20 minutes to fully penetrate and destroy the organisms embedded in the material.
3. Pressure wash the surface. Using the right PSI for the surface type, the technician rinses away the dead growth, dirt, and staining. Concrete can handle higher pressure, while pavers and natural stone require a gentler touch to avoid damage.
4. Final rinse and inspection. The entire deck gets a thorough rinse, and the technician checks for any remaining spots that may need a second treatment.

Professional cleaning removes the black spots you can see and kills the roots you cannot see. This is the key difference between a surface scrub and a treatment that actually lasts.

How to Prevent Black Spots From Coming Back

Cleaning your pool patio is only half the battle. Without the right prevention steps, those black spots will return. Here is how to keep your pool deck cleaner for longer:

• Improve drainage. Make sure water flows away from the pool deck and does not puddle in low spots. Standing water is one of the biggest causes of rapid algae and mold growth.
• Trim back landscaping. Cut back trees, shrubs, and overhanging branches that shade the pool patio. More sunlight helps the surface dry faster and slows biological growth.
• Keep the deck clear of debris. Leaves, dirt, pollen, and organic matter feed mold and algae. Sweep or blow off your pool deck regularly to remove their food source.
• Fix splash and drainage issues. If your pool overflows during rain or the deck stays wet from a leaky pool pump, fix the source of the water. Less moisture means less growth.
• Seal porous surfaces. Applying a penetrating sealer to concrete or pavers fills the tiny pores and makes it harder for algae and mold to take root. A good sealer also makes the surface easier to clean going forward. If your pool deck pavers are ready for a fresh seal, use our Paver Sealing and Stripping Cost Calculator to get a personalized price estimate based on your area size, paver type, and condition.
• Schedule regular cleanings. An annual or bi-annual professional wash prevents black spots from ever building up to the point where they become a major problem. Regular maintenance is always more affordable than waiting for a full restoration cleaning.

Do Not Let Black Spots Ruin Your Pool Patio

Black spots on your pool patio are more than just an eyesore. Algae, mold, and mildew make the surface slippery and dangerous, especially when wet. They also break down concrete, erode paver joints, and stain natural stone over time. The longer you wait to address them, the deeper they embed into the surface and the harder they become to fully remove.

Hydro Wash 360 specializes in pool patio cleaning for homeowners across Jacksonville, St. Augustine, Ponte Vedra, Orange Park, Fleming Island, and the surrounding areas of Northeast Florida. We use professional-grade cleaning solutions and the right pressure for every surface type to kill black spots at the root and restore your pool deck to like-new condition.

Ready to get rid of those black spots for good? Contact Hydro Wash 360 today for a free quote. We will get back to you the same day.