Addressing Algae Problems in Gunite Pools
Algae growth in a swimming pool is one of the most frustrating maintenance issues for homeowners, especially when you’ve invested in a high-end, custom gunite pool. While gunite offers superior durability and beauty, its porous surface can make it more vulnerable to algae buildup if not properly maintained.
In this guide, we’ll cover everything you need to know about addressing algae problems in gunite pools—from understanding why it happens, how to prevent it, and most importantly, how to get rid of it when it strikes.
💧 Why Algae Grows in Gunite Pools
Algae are microscopic aquatic organisms that thrive in warm, nutrient-rich water, especially when there’s poor circulation or inadequate sanitizer levels. Gunite pools, with their plaster or pebble finishes, offer small surface imperfections where algae spores can attach and grow if conditions allow.
Common causes of algae growth:
Low chlorine levels or inconsistent sanitation
Poor circulation or dead spots in the water flow
Warm water temperatures
Improper pH or water balance
Debris and organic matter left in the pool
Lack of brushing on porous surfaces
🧪 Even if your water looks clear, algae can be hiding in small cracks or textured areas of your gunite finish.
🌿 Types of Pool Algae
To properly treat and prevent algae, it’s helpful to identify which type you’re dealing with:
1. Green Algae
Most common and fastest-growing
Makes water cloudy or greenish
Often floats or sticks to pool walls
2. Yellow (Mustard) Algae
Appears as yellow or brown dust on walls and floors
Typically found in shaded areas
More resistant to chlorine than green algae
3. Black Algae
Toughest to eliminate
Appears as black spots with protective layers
Roots deeply into gunite pool surfaces
🦠 Black algae is especially aggressive in gunite pools due to its ability to anchor into porous plaster and pebble finishes.
🧼 How to Remove Algae from Your Gunite Pool
Step 1: Test and Balance Water Chemistry
Use a reliable test kit to check:
Chlorine levels (should be 1–3 ppm)
pH (ideal range: 7.2–7.6)
Alkalinity (80–120 ppm)
Cyanuric acid (stabilizer, 30–50 ppm)
Adjust water chemistry as needed before shocking the pool.
Step 2: Brush the Entire Pool Surface Thoroughly
Use a stiff, nylon-bristle brush designed for gunite or plaster finishes.
Brush all walls, floors, steps, and corners
Pay special attention to areas with visible algae
Brushing disrupts algae’s protective layer and exposes it to sanitizers
🧽 Don’t forget behind ladders, lights, and skimmers—algae love hiding there.
Step 3: Shock the Pool
Use a chlorine-based pool shock, such as calcium hypochlorite.
For green algae: double or triple the normal shock dose
For mustard algae: triple shock, possibly with an algaecide
For black algae: heavy shock plus brushing multiple times daily
Let the pump run continuously for 24–48 hours after shocking.
Step 4: Use a Specialized Algaecide (Optional but Helpful)
Choose an algaecide based on the algae type:
Quaternary ammonia for green algae
Copper-based algaecide for yellow or mustard algae
Polyquat or silver algaecide for black algae
Follow manufacturer instructions closely.
Step 5: Vacuum and Clean the Filter
Manually vacuum dead algae to waste (bypass the filter)
Backwash or clean your pool filter thoroughly
Repeat if necessary until the pool is clear
🔁 Prevention: Keeping Algae Out of Your Gunite Pool
An ounce of prevention is worth a pound of shock treatment. Here’s how to keep algae away from your pool long-term:
✅ Maintain Proper Chlorine Levels
Use a chlorine floater, salt system, or automated feeder to keep sanitizer levels steady.
✅ Balance Water Chemistry Weekly
Keeping pH, alkalinity, and stabilizer levels in range helps chlorine work more effectively.
✅ Brush Weekly, Especially in Shady or Low-Circulation Areas
Even if the pool looks clean, brushing helps eliminate microscopic spores.
✅ Run the Pump Long Enough Daily
Circulation is key to preventing dead spots where algae can grow. Aim for 8–12 hours per day, depending on the season.
✅ Shock the Pool After Heavy Use or Rain
Chlorine demand spikes after:
Pool parties
Storms
High heat days
Shock regularly to prevent algae from getting a foothold.
✅ Keep Debris Out
Leaves, dirt, and sunscreen all contribute to algae-friendly conditions. Skim and vacuum often.
🛠️ Gunite Surface Considerations
Because gunite pools often feature rougher surfaces like plaster or exposed aggregate, they may require more frequent brushing and water balancing than smooth-surface vinyl or fiberglass pools.
If your pool finish is aging, consider acid washing or resurfacing to remove stubborn algae stains and improve resistance to future growth.
🏡 Get Expert Pool Service with Harpeth Valley Hardscape
At Harpeth Valley Hardscape, we build and maintain high-quality gunite pools throughout Middle Tennessee. We understand the challenges that come with caring for a gunite surface—and we offer the expertise to help you prevent, treat, and eliminate algae problems for good.
From pool start-up and seasonal maintenance to long-term solutions like automation systems, resurfacing, or smart chlorination, our team is here to make pool ownership stress-free.
📋 Fill out the form below to schedule a consultation or pool health checkup today.
