Why Is My Pool Green? Causes, Solutions & Prevention

Waking up to a green pool is frustrating and alarming. The good news? Green pool water is fixable, and understanding the cause helps prevent it from happening again. This guide explains why pools turn green and provides actionable solutions.

Quick Answer: Why Pools Turn Green

Green pool water is caused by algae growth. Algae thrives when:

• Chlorine levels drop too low (below 1 ppm)
• Poor water circulation allows algae to settle
• Unbalanced pH and alkalinity reduce chlorine effectiveness
• Phosphates (algae food) accumulate in water
• Pool isn't brushed or cleaned regularly

In Central Florida, green pools are especially common after:

• Summer thunderstorms (dilute pool chemistry)
• Extended absences (missed maintenance)
• Equipment failures (pump or chlorinator stops working)
• Heavy pool usage without adequate chemical maintenance

Types of Green Pool Water

Light Green (Early Algae)

Appearance: Slightly cloudy with greenish tint Cause: Early-stage algae growth, just starting Fix Time: 24-48 hours Severity: Easy fix

Medium Green (Established Algae)

Appearance: Clearly green, can't see pool bottom clearly Cause: Several days of algae growth Fix Time: 3-5 days Severity: Moderate effort required

Dark Green (Severe Algae)

Appearance: Swamp-like, can't see bottom at all Cause: Weeks of neglect, severe algae bloom Fix Time: 5-7 days or more Severity: Professional help recommended

Step-by-Step Solution to Clear Green Pool

Step 1: Test Your Water

Why: You need to know current chemistry to calculate chemical needs

Test for:

• pH level
• Alkalinity
• Chlorine (probably zero)
• Phosphates (if possible)

Don't skip this step. Without accurate readings, you're guessing at chemical amounts.

Step 2: Remove Large Debris

Before adding chemicals:

• Skim all surface debris
• Remove leaves and large items
• Empty skimmer baskets
• Empty pump basket

Why: Large debris interferes with circulation and treatment.

Step 3: Brush the Entire Pool

Brush aggressively:

• All walls from top to bottom
• Pool floor
• Steps and benches
• Behind ladders and fixtures

Why: Brushing dislodges algae from surfaces so chemicals can kill it. This is the most overlooked step but critically important.

Step 4: Balance pH and Alkalinity

Target ranges:

• pH: 7.2-7.4 (lower end better for shocking)
• Alkalinity: 80-120 ppm

Why: Proper pH ensures shock treatment works effectively. High pH wastes chlorine.

How to adjust:

• Lower pH: Add muriatic acid
• Raise pH: Add soda ash
• Raise alkalinity: Add baking soda

Step 5: Shock the Pool

This is the critical step.

How much shock to add:

• Light green: 2-3 lbs per 10,000 gallons
• Medium green: 4-5 lbs per 10,000 gallons
• Dark green: 6-8 lbs per 10,000 gallons

Best shock to use:

• Calcium hypochlorite (cal-hypo) for speed
• Liquid chlorine for no calcium increase
• Avoid dichlor/trichlor (increases stabilizer)

Shocking tips:

• Shock at dusk/night (sunlight degrades chlorine)
• Spread evenly around pool
• Keep pump running 24 hours
• Test chlorine after 6-8 hours

Goal: Achieve 30 ppm chlorine (yes, very high - this kills algae)

Step 6: Run Pump Continuously

How long: 24-48 hours minimum

Why: Circulation distributes chemicals and filters dead algae.

Important: Clean or backwash filter every 8-12 hours. Dead algae clogs filters quickly.

Step 7: Brush Again (And Again)

Next 24-48 hours:

• Brush pool at least 2-3 times
• Every time you pass the pool, brush it
• Focus on areas where algae was worst

Why: Dead algae settles to bottom. Brushing keeps it suspended so filter can remove it.

Step 8: Vacuum to Waste

After 24-48 hours:

• Vacuum pool to waste (not to filter)
• This removes dead algae without clogging filter
• Backwash sand or DE filters thoroughly

If you don't have waste setting:

• Vacuum to filter
• Clean/backwash filter immediately after
• Repeat if needed

Step 9: Maintain High Chlorine

For next 3-5 days:

• Keep chlorine at 5-10 ppm
• Test twice daily
• Add chlorine as needed to maintain level

Why: Ensures all algae is completely killed. Lowering chlorine too soon allows algae to return.

Step 10: Address Root Cause

Once clear, prevent recurrence:

• Test and balance water weekly
• Maintain 2-3 ppm chlorine always
• Brush weekly minimum
• Run pump 8-12 hours daily
• Consider phosphate remover if needed

Common Mistakes to Avoid

1. Not Brushing Enough

The Problem: Algae clings to surfaces. Chemicals alone can't reach it effectively. The Fix: Brush, brush, brush. More than you think necessary.

2. Adding Too Little Shock

The Problem: Insufficient chlorine lets algae survive and regrow. The Fix: Calculate shock amount based on pool size and algae severity. Don't guess.

3. Not Running Pump Long Enough

The Problem: Chemicals can't circulate, dead algae settles. The Fix: Run pump 24 hours continuously during treatment.

4. Not Cleaning the Filter

The Problem: Clogged filter reduces circulation and prolongs clearing time. The Fix: Clean/backwash filter every 8-12 hours during treatment.

5. Swimming Too Soon

The Problem: High chlorine levels are unsafe. Disturbing treatment process slows clearing. The Fix: Wait until chlorine drops below 5 ppm before swimming.

6. Giving Up Too Early

The Problem: Water looks worse before it looks better (dead algae clouds water). The Fix: Trust the process. Keep brushing, filtering, and maintaining chlorine.

Prevention: Keep Your Pool from Turning Green

Maintain Proper Chlorine

Target: 2-3 ppm free chlorine at all times Test: 2-3 times per week minimum Boost: After storms, heavy usage, or hot weather

Brush Weekly

Why: Prevents algae from establishing on surfaces Focus areas: Shaded areas, behind ladders, steps, corners

Run Pump Adequately

Summer: 10-12 hours daily Winter: 6-8 hours daily Goal: Complete water turnover twice daily

Balance Water Chemistry

Weekly testing:

• pH: 7.2-7.6
• Alkalinity: 80-120 ppm
• Stabilizer: 30-50 ppm

Monthly testing:

• Calcium hardness
• Phosphates

Clean Filter Regularly

Schedule:

• Cartridge: Monthly cleaning, replace yearly
• Sand: Backwash weekly, replace media every 5-7 years
• DE: Backwash as needed, recharge with DE

Address Phosphates

What: Algae food that accumulates from rain, leaves, debris Solution: Use phosphate remover quarterly or as needed Test: Phosphate levels should be below 200 ppb

When to Call a Professional

Call us if:

• Pool is dark green/black (severe algae)
• You've tried clearing it but algae returns
• Equipment isn't working properly
• You don't have time for multi-day treatment process
• Pool has been neglected for months

We offer emergency green pool cleanup:

• Typically clear in 24-48 hours
• Professional-grade chemicals and equipment
• Complete water balance restoration
• Identify and fix underlying problems

Cost Considerations

DIY Green Pool Treatment

Chemicals needed:

• Shock (cal-hypo): $30-$80
• pH decreaser (muriatic acid): $10-$20
• Algaecide (optional): $20-$40
• Phosphate remover (optional): $25-$50 Total DIY cost: $50-$150

Your time investment: 10-20 hours over several days

Professional Service

Typical cost: $200-$600 depending on severity Includes:

• All chemicals
• Equipment and labor
• Typically 24-48 hour turnaround
• Water balance restoration
• Problem diagnosis

Worth it when: Time is limited, pool is severely green, or DIY attempt failed

Central Florida Specific Considerations

Summer Storms

Challenge: Heavy afternoon rains dilute pool chemistry rapidly Solution: Test and adjust chemicals after every major storm. Keep extra chlorine on hand.

High UV Exposure

Challenge: Intense Florida sun depletes chlorine quickly Solution: Maintain cyanuric acid (stabilizer) at 40-50 ppm to protect chlorine from UV.

Year-Round Pool Season

Challenge: Algae never has an "off season" in Florida Solution: Maintain consistent maintenance schedule year-round, not just summer.

Warm Water Temperatures

Challenge: Algae thrives in warm water (above 80°F) Solution: Higher chlorine levels needed in summer. Test more frequently during hot weather.

FAQ: Green Pool Questions

Q: Can I swim in a slightly green pool? A: No. Green water means algae is present, which harbors bacteria. Wait until pool is clear and chlorine is below 5 ppm.

Q: How long does it take to clear a green pool? A: Light green: 1-2 days. Medium green: 3-5 days. Dark green: 5-7 days or more. Professional service typically 24-48 hours.

Q: Will shocking damage my pool? A: No. Shocking is safe for all pool types when done correctly. Don't shock vinyl pools during day (sunlight can bleach liner).

Q: Can I use algaecide instead of shock? A: No. Algaecide prevents algae but doesn't kill established blooms. Shock (high chlorine) is required to kill algae. Algaecide can be used after as prevention.

Q: Why does my pool keep turning green? A: Recurring green pools indicate underlying problems: inadequate chlorine maintenance, poor circulation, high phosphates, or equipment malfunction.

Q: Is green pool water dangerous? A: While algae itself isn't usually toxic, green water harbors bacteria and can mask hazards like broken tiles or depth changes. Don't swim until treated.

Conclusion

Green pools are frustrating but fixable with proper treatment and patience. The key is aggressive shocking, constant brushing, continuous filtration, and addressing the root cause to prevent recurrence.

Need help clearing your green pool fast? Central Florida Pool & Spa offers emergency green pool cleanup throughout Osceola, Orange, and Polk Counties. We'll have your pool sparkling clear in 24-48 hours. Call (863) 353-6873 for immediate assistance.

Don't waste your summer with a green pool—get it fixed right the first time.