Pool Care Blog
Why Is My Pool Green? (And How to Fix It Fast)
Pool Problems · March 5, 2026 · 5 min read
You walk outside expecting a sparkling blue pool — and instead you're staring at something that looks like a swamp. It happens to thousands of Houston-area homeowners every year, especially between March and October when temperatures climb and algae thrive.
The good news? A green pool is almost always fixable. The bad news? The longer you wait, the harder and more expensive it gets. Here's exactly what's happening in your water and what to do about it.
What Causes a Pool to Turn Green?
The short answer is algae — microscopic plant organisms that multiply explosively when conditions are right. Your pool becomes a buffet when three things happen at the same time: chlorine drops below 1 ppm, water temperature exceeds 60°F, and there's any organic matter to feed on (leaves, pollen, body oils).
In Greater Houston, our subtropical climate means pools are vulnerable almost year-round. A single afternoon thunderstorm can dump enough rainwater to dilute your chlorine, shift your pH, and introduce phosphates — triggering algae growth within 24 hours.
The Three Types of Pool Algae
Green Algae (most common)
Free-floating algae that turns water cloudy green. Usually the easiest to treat — responds well to shock treatment and brushing. This is what 80% of Houston homeowners deal with.
Yellow / Mustard Algae
Clings to walls and shady areas. Looks like sand or pollen deposits. Chlorine-resistant — requires specialized algaecide and aggressive brushing to eliminate.
Black Algae
The most stubborn type. Roots deep into plaster and grout. Appears as dark spots on pool surfaces. Often requires professional treatment and sometimes replastering of affected areas.
Technician Tip
Before you shock a green pool, always brush the walls and floor first. Algae has a protective biofilm layer that chlorine can't penetrate. Brushing breaks that barrier and lets the shock do its job 3x faster.
The Professional Green Pool Recovery Process
DIY shock treatments from the pool store work for mild cases. But if you can't see the bottom of your pool, you're past the point where a single bag of shock will fix things. Here's the process our PHTA-certified technicians follow:
Test & Diagnose
We test chlorine, pH, alkalinity, CYA, and phosphates to understand exactly why the algae took hold — not just treat the symptom.
Heavy Shock Treatment
We calculate the exact amount of chlorine needed for your pool's volume and algae severity. Typically 3–5x normal shock dose for a fully green pool.
Brush Every Surface
Algae clings to walls, steps, and crevices. Manual brushing breaks its grip so chemicals can penetrate and kill it.
Run Filtration 24/7
The filter needs to run continuously for 48–72 hours to capture dead algae. We clean or backwash the filter multiple times during this process.
Vacuum Dead Algae
Once the water turns cloudy blue/gray (dead algae), we vacuum it out — often straight to waste to avoid clogging the filter.
Balance & Prevent
Final chemistry balancing plus recommendations to keep it from happening again. Usually involves adjusting your chlorine delivery method or run times.
Want your green pool handled fast? Admiral Pool Service typically restores clear water in 3–5 days.
Get a Green Pool Quote →How Long Does It Take?
Most green pools go from green to swim-ready in 3–5 days. Severe swamp-level cases with black algae or pools that have been neglected for months can take 5–7 days — and extreme cases 2+ weeks. The key factor is how quickly the filter can process the dead algae — which is why we sometimes recommend a temporary filter upgrade for the worst cases.
Preventing It From Coming Back
Maintain chlorine between 2–4 ppm at all times
Run your pump at least 8–12 hours per day in summer
Brush walls and waterline weekly
Keep phosphate levels below 300 ppb
Clean your filter every 3–6 months
Address chemistry imbalances within 24 hours
Need Professional Pool Help?
Admiral Pool Service has been keeping Greater Houston pools crystal clear since 2019. Licensed, insured, and PHTA certified.
Or call (281) 624-6191.
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