You’ve shocked the pool. You’ve added algaecide. The water chemistry looks balanced. But day after day, your pool is still a stubborn shade of green. Sound familiar?

This is one of the most common and frustrating problems pool owners face. Fortunately, green pool water isn’t just a mystery; it’s a symptom of a larger issue. And once you understand what’s really going on, you can take action that actually works.

Why Do Pools Turn Green in the First Place?

Green water is usually a sign of algae growth. Algae thrive in warm, stagnant water, especially when chlorine levels drop or become ineffective. The color intensity can give clues about the severity of the issue:

• Light green: Early algae bloom or slight imbalance
• Dark, murky green: Advanced algae infestation or filtration failure

Sometimes, though, metals like copper or iron can also turn your pool green, especially after shocking it.

Top Reasons Your Pool Stays Green

When your pool stays green despite treatment, it’s often because one or more underlying issues are being overlooked. Here are the most common reasons your pool water won’t clear up.

Your Chlorine Isn’t Working Effectively

Even if your chlorine levels seem normal, they might not be killing algae. Why?

• High chlorine demand: Rain, sun, and organic debris exposure can deplete chlorine faster than it can sanitize.
• Incorrect shocking: Not using enough shock, or using stabilized chlorine when unstabilized is needed, reduces effectiveness.
• Chlorine lock: A chemical imbalance (often from high cyanuric acid) that prevents chlorine from doing its job.

Poor Water Circulation

Algae loves areas of your pool where water does not properly circulate, known as dead zones.

• Your pump may not be running long enough (aim for 8–12 hours/day).
• Filters or skimmers may be clogged.
• Return jets may be angled poorly, limiting flow.

Filtration Problems

Your filter is the frontline defense against algae. If it’s not working right, algae stays suspended in the water.

• Sand filters can get channeling and need deep cleaning or replacement.
• Cartridge filters clog easily and require regular rinsing or replacement.
• DE filters offer fine filtration but can lose efficiency over time.

Imbalanced Water Chemistry

pH, total alkalinity, and cyanuric acid (stabilizer) all affect chlorine performance.

• High pH or alkalinity can reduce chlorine’s ability to sanitize.
• Too much stabilizer (CYA) locks up chlorine.
• Regular, accurate testing with a liquid test kit is crucial.

Metal Contamination

If your water turned green after shocking it, metals may be to blame.

• Copper or iron in the water can oxidize when chlorine is added.
• This is more common in areas with hard water or older copper pipes.
• Use a metal sequestrant to bind metals and prevent discoloration.

Common Pool Maintenance Mistakes That Make Algae Worse

• Not brushing the pool walls and floor: Algae clings to surfaces and won’t die off with chemicals alone.
• Relying on a single shock: Severe algae needs multiple treatments over time.
• Skipping filter maintenance: Dirty filters recirculate algae.
• Trusting unreliable test strips: Use a proper liquid test kit or take a sample to a pool store.

How to Finally Clear Your Green Pool Water

Follow this step-by-step plan:

1. Remove debris with a net and vacuum.
2. Brush all pool surfaces thoroughly.
3. Test and balance water, adjusting the pH to 7.2–7.4 for best chlorine performance.
4. Shock the pool using the right type and quantity (aim for 10 ppm free chlorine).
5. Run the pump continuously for 24–48 hours.
6. Clean or backwash the filter.
7. Use a clarifier or flocculant to help filter out dead algae.
8. Monitor chlorine levels daily until the water clears.

Persistent green pool water can be frustrating, but it’s almost always fixable with the right combination of chemistry, circulation, and filtration. Identifying the underlying cause, rather than relying on repeated treatments, will ultimately save you time, money, and stress.

If you’re still battling cloudy or green water, let the experts at Lucas Firmin Pools help. Our team specializes in quickly and professionally diagnosing and restoring pool water clarity. Contact us today for a customized solution and get your pool back to crystal clear.