Water Testing for Natural Pools: Complete UK Guide

Why Water Testing Matters for Natural Pools

Unlike chlorinated pools where you're testing chemical levels, natural swimming pool testing focuses on the health of your living ecosystem. Understanding the underlying science helps you appreciate why different parameters matter—and why testing is simpler than you might expect.

Regular monitoring ensures your regeneration zone is working effectively and catches any imbalances before they become visible problems. Testing costs are part of the overall complete cost breakdown for running your natural pool. When issues arise, qualified pool designers can help diagnose problems and recommend solutions.

Key Parameters to Monitor

pH Level

Target range: 6.5 - 8.5 Natural pools are more forgiving than chlorinated pools, but pH still matters:

• Affects plant health and nutrient uptake
• Influences beneficial bacteria activity
• Impacts swimmer comfort

Most UK natural pools naturally sit around 7.0-7.5, which is ideal. If pH drifts consistently outside this range, investigate the cause rather than adding chemicals.

Ammonia (NH₃/NH₄⁺)

Target: 0 - 0.25 mg/L Ammonia is the first product of organic breakdown. Elevated levels indicate:

• Overloading from organic debris
• Insufficient bacterial activity
• New pool still establishing

See our nitrogen cycle guide for how ammonia converts to safer compounds.

Nitrite (NO₂⁻)

Target: 0 - 0.1 mg/L Nitrite is the intermediate step in nitrogen processing. High readings suggest:

• Incomplete nitrogen cycling
• Bacterial population under stress
• Temperature fluctuations affecting bacteria

This is a critical parameter for new pools during their first season.

Nitrate (NO₃⁻)

Target: Below 25 mg/L The end product of the nitrogen cycle. Plants absorb nitrates as fertiliser. High levels indicate:

• Excellent bacterial activity (good!)
• Plants may need thinning
• Possible external nutrient sources

Phosphate (PO₄)

Target: Below 0.03 mg/L The key nutrient for algae growth. See our complete phosphate control guide for management strategies. Sources include:

• Decomposing organic matter
• Garden fertiliser runoff
• Tap water (varies by region)
• Swimmer sunscreen

Dissolved Oxygen

Target: Above 6 mg/L Essential for beneficial bacteria and overall ecosystem health:

• Oxygenating plants boost levels
• Low oxygen causes anaerobic conditions
• Critical in warm summer months

Testing Frequency

Weekly (During Swimming Season)

• pH
• Visual clarity check
• Surface debris assessment

Fortnightly (Peak Summer)

• Ammonia
• Nitrite
• Phosphate

Monthly

• Nitrate
• Dissolved oxygen
• Full visual inspection of regeneration zone

Spring & Autumn

• Complete test of all parameters
• Record baseline readings

DIY Test Kits vs Professional Testing

DIY Strip Tests (£15-30)

Best for: Weekly pH monitoring

• Quick and convenient
• Less accurate
• Good for trend spotting

DIY Liquid Test Kits (£30-80)

Best for: Fortnightly nitrogen testing

• More accurate than strips
• Colour matching can be subjective
• Good value for regular use

Digital Testers (£50-200)

Best for: pH and dissolved oxygen

• Very accurate
• Require calibration
• Worth the investment for pH

Professional Lab Testing (£50-150)

Best for: Annual comprehensive analysis

• Laboratory accuracy
• Tests for additional parameters
• Baseline comparison year-on-year
• Recommended once per season

Interpreting Results

Healthy Pool Indicators

• Stable pH between 6.8-7.8
• Zero or trace ammonia/nitrite
• Low phosphate
• Clear water with natural tint
• Active, healthy plants

Warning Signs

| Parameter | Warning Level | Action | |-----------|--------------|--------| | pH | Below 6.0 or above 9.0 | Investigate source water | | Ammonia | Above 0.5 mg/L | Reduce organic load, check circulation | | Nitrite | Above 0.25 mg/L | Boost aeration, check pump function | | Phosphate | Above 0.1 mg/L | Remove sources, add phosphate-binding plants |

Seasonal Considerations

Spring

Expect elevated readings as the ecosystem awakens. Bacterial activity increases with temperature. Patience is key.

Summer

Peak biological activity. Test more frequently during hot spells when oxygen levels can drop.

Autumn

Falling leaves add organic load. Increase debris removal and monitor ammonia.

Winter

Minimal testing needed. One check per month to ensure no major issues.

When to Call a Professional

Contact your natural pool specialist if you see:

• Persistent cloudy water despite good readings
• Fish or wildlife die-off
• Strong unusual odours
• Readings consistently outside ranges
• Sudden dramatic changes

Recording Your Results

Keep a simple log book or spreadsheet:

• Date and time
• Weather conditions
• All test results
• Any observations
• Actions taken

This history helps identify trends and troubleshoot issues. It's also valuable if you sell your home and need to demonstrate the pool's maintenance history.

The Lume Approach

Every Lume pool includes a comprehensive testing kit and first-year guidance. We teach you to read your pool's natural rhythms so testing becomes intuitive rather than anxious.

Start your natural pool journey with our free AI visualisation tool to see what's possible in your garden.