Pool Chemical Dosing Chart

How to Use a Pool Chemical Dosing Chart

Adding pool chemicals without a reference point is one of the most common reasons pools end up out of balance. Too little and the water stays unsafe. Too much and you risk irritating swimmers, damaging equipment, or sending the chemistry further off course.

This guide covers the main chemicals used in a residential pool, what the target ranges are, and how to approach dosing adjustments safely.

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Why Getting the Dose Right Matters

Pool water chemistry is a balancing act. Each parameter affects the others. pH influences how effective your chlorine is. Alkalinity affects how stable your pH stays. Calcium hardness affects whether your water is aggressive or scaling.

Dosing one chemical without checking the others is a common mistake. Always test the full picture before adding anything.

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Target Ranges for Key Parameters

Before dosing anything, you need to know where your water currently sits. Test first, then act.

pH

• Target range: 7.2-7.6
• pH below 7.2 makes water acidic, it can irritate eyes and skin, and corrode equipment
• pH above 7.8 reduces chlorine effectiveness significantly and can cause cloudy water or scale

Total Alkalinity

• Target range: 80-120 ppm
• Alkalinity acts as a buffer for pH, if it's too low, pH swings wildly; if it's too high, pH becomes hard to adjust

Free Chlorine

• Target range: 1-3 ppm
• Free chlorine is your active sanitiser, it kills bacteria and algae
• Levels below 1 ppm leave the pool unprotected; above 5 ppm can irritate swimmers

Calcium Hardness

• Target range: 200-400 ppm
• Low calcium causes water to draw minerals from surfaces, leading to pitting and plaster damage
• High calcium leads to scale on surfaces and equipment

Cyanuric Acid (Stabiliser)

• Target range: 30-50 ppm
• Stabiliser protects chlorine from UV breakdown in sunlight
• Too much stabiliser reduces chlorine's ability to sanitise, this is called chlorine lock

Salt (Salt Water Pools)

• Target range: Varies by chlorinator model, check your unit's manual
• Most residential salt chlorinators operate in the range of 3,000-4,000 ppm, but confirm with your specific equipment

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How to Adjust Each Parameter

Raising pH

Use soda ash (sodium carbonate). Add it to a bucket of water first, then distribute around the pool with the pump running. Retest after a few hours.

Lowering pH

Use pH reducer (sodium bisulphate or muriatic acid). Acid is hazardous, handle with care, always add chemical to water (not water to chemical), and keep the pump running. Retest before adding more.

Raising Total Alkalinity

Use sodium bicarbonate (baking soda / alkalinity increaser). Broadcast it across the pool surface with the pump running.

Lowering Total Alkalinity

Use pH reducer, added in a concentrated spot near a return jet with the pump off. This method targets alkalinity more than pH. It requires multiple small doses and retesting between each.

Raising Free Chlorine

Use granular chlorine (calcium hypochlorite) or liquid chlorine (sodium hypochlorite). For a quick boost, called shocking, use a higher dose to break through combined chlorine or algae. Always pre-dissolve granular chlorine in a bucket before adding to the pool.

Raising Calcium Hardness

Use calcium chloride. Add slowly with the pump running. Calcium chloride generates heat when dissolved, pre-dissolve in a bucket of water before adding to the pool.

Lowering Calcium Hardness

There is no chemical that removes calcium from pool water. The only reliable fix is partial drain and refill with fresh water. This is best done with professional guidance to avoid over-diluting other parameters.

Adjusting Cyanuric Acid

Stabiliser can only be raised, add cyanuric acid granules directly to the skimmer with the pump running. To lower stabiliser, you need to dilute the pool water with a partial drain and refill.

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General Dosing Rules

• Always test before dosing. Never add chemicals based on guesswork or a fixed schedule alone.
• Add one chemical at a time. Wait and retest before adding the next. Mixing effects makes it hard to know what worked.
• Never mix chemicals together, not in a bucket, not in the pool, not in storage. Some combinations are dangerous.
• Add chemicals with the pump running so they distribute evenly.
• Pre-dissolve granular chemicals in a bucket of pool water before broadcasting, unless the product label says otherwise.
• Retest after 4-6 hours (or after the next full pump cycle) before making further adjustments.
• Dose in small increments. It is easier to add more than to correct an overdose.

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How Pool Size Affects Dosing

All chemical doses are calculated per volume of water. A standard residential pool in New Zealand is typically somewhere between 40,000 and 80,000 litres, but pools vary considerably.

If you do not know your pool's volume, calculate it:

• Rectangular pool: Length × Width × Average Depth × 1,000 (for litres)
• Circular pool: Radius × Radius × 3.14 × Average Depth × 1,000

Always check the product label for the recommended dose per 10,000 litres (or per the unit stated on the packaging), then scale up to your pool's volume.

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When Auckland Conditions Affect Dosing

Auckland's climate means pools are often used year-round, and the warmer months bring specific challenges:

• High UV in summer burns through chlorine faster, stabiliser levels become more important
• Heavy rain dilutes chemicals and can introduce phosphates and organic matter, dropping chlorine levels quickly
• Warm water accelerates algae growth and increases chlorine demand
• Bather load, more swimmers means more organic matter and faster chlorine consumption

After heavy rain or a busy weekend of swimming, test and adjust rather than waiting for your regular schedule.

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When to Get Professional Help

Some situations are harder to correct without experience:

• Persistent algae that returns after shocking, the underlying cause (stabiliser too high, circulation issues, phosphates) needs diagnosing
• Chlorine that won't hold despite regular dosing, this often points to combined chlorine, high stabiliser, or a chlorinator fault
• Repeated pH instability, if pH swings constantly, alkalinity or stabiliser may be out of range
• Staining or scale, these can require specific treatments and the wrong approach can make them worse
• You're not sure what's wrong, a professional water test gives a full picture and a clear action plan

Sparkling Pools offers on-site water testing across Auckland. A technician comes to your home, tests the water on site, and advises on exactly what needs adjusting.

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A Note on Product Labels

This guide provides general reference ranges. Always read the label on the specific product you are using, concentrations vary between brands, and the label dose is the one that applies to your product. When in doubt, dose conservatively and retest.