What Is pH and Why Does It Matter?
pH measures how acidic or alkaline your pool water is, on a scale from 0 to 14. A pH of 7 is perfectly neutral. Below 7 is acidic, above 7 is alkaline. Your pool should sit between 7.2 and 7.6 — slightly alkaline — for two key reasons:
- Chlorine effectiveness: At pH 7.2–7.6, your chlorine works at about 50–75% efficiency. Above pH 8.0, it drops to under 20%. You're basically throwing money into the pool.
- Swimmer comfort: Human eyes have a pH of around 7.4. Water in the right range feels gentle. Too acidic and it stings. Too alkaline and it feels soapy and leaves residue.
The Professor's Rule: Never add chlorine to a pool with pH above 7.8. Wait until you've corrected the pH first — otherwise the chlorine is largely wasted.
Pool pH Quick Reference
Here's a reference table for every key water chemistry measurement — not just pH:
| Parameter | Ideal Range | Too Low | Too High |
|---|---|---|---|
| pH | 7.2 – 7.6 | Corrosive, eye irritation | Cloudy water, poor chlorine |
| Free Chlorine | 1 – 3 ppm | Algae growth | Bleaching, skin irritation |
| Total Alkalinity | 80 – 120 ppm | pH swings wildly | pH hard to lower |
| Calcium Hardness | 200 – 400 ppm | Corrosive to surfaces | Scale & calcium buildup |
| Cyanuric Acid | 30 – 50 ppm | Chlorine burns off fast | Chlorine effectiveness drops |
Step 1 — Test Your Pool's pH
Before you add a single chemical, you need to know where your pH actually sits. There are three ways to test:
- Test strips — cheapest option, less accurate, good for weekly checks. Dip in water, compare to the colour chart. Available at Bunnings, Pool Shops, and online.
- Drop test kit — more accurate. Add a few drops of reagent to a water sample and compare colour. Used by most professionals.
- Digital pH meter — most accurate, most expensive. Calibrate it regularly. Worth it if you test frequently.
Test at elbow depth, away from return jets and the skimmer box. Do it before adding any chemicals, and ideally at the same time each day (morning is best — before the sun burns off chlorine).
Important: Always test after any heavy rain or large number of swimmers — both events significantly shift your pool's chemistry. In Queensland and NSW summers, check twice a week minimum.
Step 2A — How to Raise pH (If pH is Below 7.2)
Low pH (acidic water) is harsh on your pool surfaces, equipment, and eyes. It also corrodes metal fittings. To raise pH, you add an alkaline substance. The two most common options are:
- Soda Ash (Sodium Carbonate) — raises pH quickly, has less effect on total alkalinity. This is the preferred choice if your alkalinity is already in range.
- Sodium Bicarbonate (Bicarb Soda) — raises alkalinity more than pH. Use this if both your pH and alkalinity are low.
Dosage for Soda Ash
As a rough guide for a standard 50,000 litre pool:
- pH 7.0 → 7.4: Add approximately 200g of soda ash
- pH 6.8 → 7.4: Add approximately 350g of soda ash
- pH 6.5 → 7.4: Add approximately 500g of soda ash
Always dissolve the powder in a bucket of pool water first before adding it. Never add chemicals directly to the pool in dry form near the pool wall or surface. Add near a return jet so it circulates, then run the pump for at least 4 hours before re-testing.
Step 2B — How to Lower pH (If pH is Above 7.8)
High pH is extremely common in Australian pools, especially those filled with bore water or high-alkalinity town water. To lower pH, you add an acid. You have two options:
- Muriatic Acid (Hydrochloric Acid) — the most effective and widely available. Handle with care — it's corrosive. Wear gloves and eye protection.
- Dry Acid (Sodium Bisulphate) — safer to handle, easier to store. Works slightly slower. Good choice for families with children.
Safety first: Always add acid to water, never water to acid. Pour muriatic acid slowly into a bucket of water, then pour the solution around the pool's deep end with the pump running. Never add acid near the shallow end, steps, or any pool surface directly.
Dosage for Muriatic Acid
For a standard 50,000 litre pool:
- pH 8.0 → 7.4: Add approximately 150ml of muriatic acid
- pH 8.5 → 7.4: Add approximately 300ml of muriatic acid
- pH 9.0 → 7.4: Add approximately 500ml of muriatic acid
These are approximate starting points. Always retest after 4–6 hours and adjust as needed. Never add the full dose at once — add half, test, then add more if needed.
Step 3 — Check Total Alkalinity Too
pH and Total Alkalinity (TA) are closely linked. Total Alkalinity acts as a buffer that prevents pH from swinging wildly. If your TA is out of range, your pH will be extremely difficult to keep stable — you'll chase it all week.
Target: 80–120 ppm. If TA is low, pH drops quickly and keeps bouncing around. If TA is high, pH is stubborn and hard to lower even with acid.
Always balance Total Alkalinity before trying to balance pH — it makes the whole process much easier.
Step 4 — Keep It Balanced With a Weekly Routine
The good news is that once balanced, pool pH is fairly easy to maintain with a simple weekly habit:
- Test pH and chlorine every 7 days (twice per week in summer or after heavy use)
- Make small adjustments — never overcorrect
- Run the pump for at least 8 hours per day in summer, 4–6 hours in winter
- Brush pool walls weekly to prevent algae taking hold
- Do a full 5-parameter test once a month (pH, chlorine, alkalinity, calcium hardness, cyanuric acid)
Pro tip: Rain dilutes your pool chemicals and can drop pH significantly. After any decent rainfall (>20mm), test and adjust before swimmers use the pool. Brisbane and coastal QLD pools especially — this catches people out every summer.
Common pH Mistakes to Avoid
- Adding too much chemical at once — always add in small doses and retest
- Testing immediately after adding chemicals — wait at least 4 hours with the pump running
- Ignoring alkalinity — fixing pH without fixing TA is a temporary fix
- Testing from the surface — always collect water from elbow depth for accurate readings
- Skipping testing in winter — yes, your pool still needs chemistry management, even if you're not swimming