# Pool Water Chemistry Explained: pH, Chlorine and Alkalinity for Auckland Pool Owners > The core numbers behind a healthy pool, and why testing beats guessing every time. Published 2026-09-29, updated 2026-10-13 Cooper's background before pool care was aircraft engineering and the fire service, and one habit carried straight over: you don't declare something fine until you've actually measured it, not just eyeballed it. Pool chemistry rewards that approach more than most people realise. A pool can look completely clear and still be out of balance, and a few numbers, tracked properly, explain almost everything that goes wrong with a pool. Here's what those numbers actually mean. ## How Often Should You Actually Test? At least once a week for a home pool, more often in summer or after heavy use, rain, or a pool party. A professional visit typically includes a full test every time, with chlorine, pH, and alkalinity as the core three. Skipping tests doesn't save time, since problems caught early are quick fixes and problems left for weeks usually aren't. We've seen what happens when that testing lapses. One pool that hadn't been properly looked after had its salt chlorinator left running at 100%, which pushed chlorine levels very high. Bringing the output back down and getting the water back into balance only happened because someone actually tested it, rather than assuming a clear-looking pool was a fine one. ## Getting pH Right Matters More Than People Think The target range is 7.2 to 7.6, with 7.4 to 7.6 the sweet spot. Below that range irritates skin and eyes and corrodes equipment over time. Above it, chlorine stops working properly even if the chlorine reading itself looks fine on the test strip. pH is the setting that makes every other chemical actually do its job, which is why it's checked first, not last. We've also come across pools where the automatic acid dosing wasn't set right, which dragged pH too low without anyone noticing until it was tested. Correcting the dosing settings and bringing pH back into range is a straightforward fix, but only once it's actually caught, which again comes back to testing rather than assuming the system is looking after itself. ## Free Chlorine vs Total Chlorine, What's the Difference? Free chlorine is the active sanitiser still available to kill bacteria and algae. Total chlorine is free chlorine plus combined chlorine, which has already reacted with contaminants in the water and isn't doing any more sanitising work. A gap between the two readings usually means it's time to shock the pool, since that combined chlorine needs to be broken down rather than left to build up. ## That Strong Chlorine Smell? It Means the Pool Needs More Chlorine, Not Less It's one of the most common misreadings in pool care. A strong chemical smell usually means too little free chlorine, not too much. The smell comes from combined chlorine, chloramines, that's already reacted with contaminants in the water, not from clean water having "too many chemicals" in it. A properly balanced pool with plenty of free chlorine available barely smells like anything at all. If a pool smells strongly of chlorine, treat it as a sign the water is dirtier than it looks, not a reason to add less next time. ## Why Total Alkalinity Is the Setting Behind the Setting Total alkalinity is the water's ability to resist pH swings, and it's easy to overlook because it doesn't show up in the water the way algae or cloudiness does. Keep it in the roughly 80 to 120 ppm range and pH stays stable and predictable. Let it drift outside that range and pH will bounce around no matter how carefully it's corrected, which is why a pool that seems to need constant pH adjustment often actually has an alkalinity problem underneath it. ## What Causes Scale Buildup Around the Pool Scale, the white, crusty deposits that show up along tile lines and on equipment, comes from high calcium hardness combined with high pH or alkalinity. It's a slow-building problem rather than a sudden one, but left untreated it can damage surfaces and clog fittings, so it's worth catching on a test rather than waiting until it's visible. ## Can Balanced Water Still Irritate Skin and Eyes? Yes, and it's usually pH, not chlorine, that's actually responsible. Irritation gets blamed on chlorine by default, but a pool can have a completely normal chlorine reading and still sting eyes or dry out skin if pH is out of range. It's another reason pH gets checked alongside chlorine rather than assumed to be fine. ## Clear Doesn't Always Mean Safe Clarity alone doesn't confirm a pool is actually safe to swim in. A pool can look completely clear while carrying unsafe bacteria levels if chlorine has dropped too low without anyone noticing, since bacteria growth doesn't always show up visually the way algae does. Regular testing, not a glance at the water, is the only reliable way to know where a pool actually stands. ## Frequently Asked Questions **How often should I test my pool water?** At least once a week for a home pool, more often in summer or after heavy use, rain, or a pool party. A professional visit typically includes a full test every time, with chlorine, pH and alkalinity as the core three. **What's the ideal pH level for a pool?** Between 7.2 and 7.6, with 7.4 to 7.6 the sweet spot. Below that range irritates skin and eyes and corrodes equipment. Above it, chlorine stops working properly even if your chlorine reading looks fine. **What's the difference between free chlorine and total chlorine?** Free chlorine is the active sanitiser still available to kill bacteria and algae. Total chlorine includes free chlorine plus combined chlorine, which has already reacted with contaminants. A gap between the two usually means it's time to shock the pool. **Why does my pool smell strongly of chlorine?** A strong chemical smell usually means too little free chlorine, not too much. It's the combined chlorine (chloramines) causing the smell, not clean water. **What is total alkalinity and why does it matter?** It's the water's ability to resist pH swings. Keep it in range, roughly 80 to 120 ppm, and pH stays stable. Let it drift and pH will bounce around no matter how much you correct it. **What causes calcium buildup (scale) around my pool?** High calcium hardness combined with high pH or alkalinity. It shows up as white, crusty deposits on tile lines and equipment, and left untreated it can damage surfaces and clog fittings. **Can pool chemicals cause skin or eye irritation even when balanced?** Yes, if pH is out of range even with correct chlorine. Irritation is often a pH problem blamed on chlorine. **Is chlorine smell a sign of a clean or dirty pool?** A strong smell usually means a dirtier pool. It comes from chloramines built up from contaminants, not from too much chlorine. **How do I know if my pool water is actually safe, not just clear?** Clarity alone doesn't confirm safety. A pool can look clear with unsafe bacteria levels if chlorine has dropped too low. Regular testing is the only reliable way to know. ## Sources - [CDC: Home Pool and Hot Tub Water Treatment and Testing](https://www.cdc.gov/healthy-swimming/about/home-pool-and-hot-tub-water-treatment-and-testing.html): recommends pH 7.0 to 7.8 and at least 1 ppm free chlorine in home pools (at least 2 ppm with cyanuric acid). The 7.2 to 7.6 target above sits inside that range. - [CDC: Preventing Eye Irritation from Pool Chemicals](https://www.cdc.gov/healthy-swimming/prevention/preventing-eye-irritation-from-pool-chemicals.html): says that if you smell 'chlorine' at the place you swim, you are probably smelling chloramines, which form when chlorine combines with sweat and other body waste. ## Related Services - [Green Pool Recovery](https://opulentpools.co.nz/green-pool-recovery) - [Filter & Media Changes](https://opulentpools.co.nz/repairs-and-installs/filter-and-media-changes) - [Salt Chlorinator Installs](https://opulentpools.co.nz/repairs-and-installs/salt-chlorinator-installs) ## See our pool maintenance plans [See our pool maintenance plans](https://opulentpools.co.nz/services) ## Get a Quote [/contact](https://opulentpools.co.nz/contact) · [021 0260 0909](tel:02102600909) · [cooper@opulentpools.co.nz](mailto:cooper@opulentpools.co.nz)