Pool Water Chemistry — The Brisbane Owner's Plain-English Guide

Pool water chemistry sounds technical but the practical version is pretty simple. Once you understand what each measurement does and what range to keep it in, you'll spend five minutes a week on it and never have a problem.

Here's the version I explain at every Wahoo handover.

The five numbers that matter

1. pH — target 7.4 to 7.6

pH is how acidic or basic the water is. Too low (under 7.2) and your eyes sting, the water etches the pebble-crete, and equipment corrodes. Too high (over 7.8) and the chlorine becomes much less effective, and calcium scale forms.

Adjust with: pH down (acid) to lower it, pH up or soda ash to raise it.

2. Free chlorine — target 1 to 3 ppm

This is the active sanitiser. Below 1 ppm, algae will appear in days. Above 3 ppm regularly, and you're wasting chlorine.

Adjust with: salt chlorinator output (turn up for more), or shock dosing if you need a fast lift.

3. Total alkalinity — target 80 to 120 ppm

Alkalinity is pH's stability backbone. When alkalinity is in range, pH stays steady. When alkalinity is low, pH bounces around with every rainfall.

Adjust with: alkalinity up (sodium bicarbonate) to raise it, slowly add muriatic acid to lower it.

4. Salt — target 3,500 to 5,000 ppm (depending on your chlorinator)

The salt is what the chlorinator converts into chlorine. The chlorinator display will tell you the current level. Top up with pool salt as needed.

Most chlorinators want 3,500-4,500 ppm. Check your manual.

5. Stabiliser (cyanuric acid / CYA) — target 30 to 50 ppm in Brisbane

Stabiliser protects chlorine from UV. In Brisbane sun, without enough stabiliser, your chlorine evaporates in hours.

Add stabiliser once at the start of each summer if levels are low. Stabiliser doesn't come out of solution — you usually only need to add it after dilution events.

What to test, how often

Weekly in summer:

• pH — always
• Free chlorine — always

Monthly:

• Total alkalinity
• Salt level

Quarterly or after a big dilution event:

• Stabiliser
• Calcium hardness

Twice a year (free at most pool shops in Brisbane):

• Phosphates, metals, complete chemistry profile

Test kits vs strips

Test strips are fast, good for weekly checks. About 80% accurate. Fine for most owners.

Liquid drop test kits (e.g. Taylor K-2006) are slower and more accurate. Worth keeping one in the shed for monthly deeper tests.

Digital testers (e.g. Spin Touch, AquaChek) are accurate, fast, and expensive. Optional for keen owners.

Many Brisbane pool shops will test your water for free — just bring 250ml in a clean bottle. Worth doing every 2-3 months for a sanity check.

What goes wrong (and how to fix)

Pool is cloudy. Usually a free chlorine issue. Test, shock if needed, run the filter for 24-48 hours. Brush the walls.

Green tinge. Algae starting. Shock chlorinate, brush thoroughly, run pump 24 hours. Add algaecide if persistent.

Eyes stinging. Almost always pH is too low. Add pH up.

Salt cell isn't producing. Check salt level (could be low), check cell for calcium (clean if scaled), check for proper flow.

Yellow or brown staining. Metals in the water. Take a sample to a pool shop, ask for metal sequestrant.

The unscientific test that works

Eye test the water. Crystal clear means chemistry is OK. Slightly cloudy means something's off — test and adjust. Trust your eyes alongside the strips.

If you've got a Wahoo pool and chemistry is misbehaving, send me a photo and the test results. We'll work it out. If you're new to pool ownership and worried about this stuff, don't be. It's genuinely a five-minute weekly thing once you've done it a few times.

— Travis