If you’ve tested your pool water and got a reading above 7.8, your pH is too high. The water is too alkaline and it needs to be corrected. Left untreated, it causes problems for swimmers, reduces how well your chlorine works, and leads to scale buildup on surfaces and equipment.
This guide covers what high pH means, why it happens, and how to fix it step by step.
pH is a measure of how acidic or alkaline your pool water is. It runs on a scale from 0 to 14. A reading of 7 is neutral. Below 7 is acidic. Above 7 is alkaline. For swimming pools, the sweet spot is between 7.2 and 7.6. That range keeps the water comfortable for swimmers and helps your chlorine do its job properly.
When pH goes above 7.8, things start to go wrong. The water becomes too alkaline. Chlorine loses a lot of its effectiveness. Bacteria and algae can start to thrive even if you think your chlorine levels are fine. Swimmers may notice stinging eyes or irritated skin. And over time, scale starts to build up on pool surfaces, tiles, and equipment. If you notice persistent surface staining or a rough texture forming, it may be worth looking into pool resurfacing down the line.
There are a few different reasons this happens. It helps to know which one applies to your situation.
Before you add anything to the water, test it. Don’t guess. You can use test strips, a liquid test kit, or a digital tester. Test strips are the easiest. They give you a reading in about a minute. But liquid test kits and digital testers tend to be more accurate if you want to be sure.
Test the water in the morning before anyone swims and before adding any chemicals. Take a sample from about elbow depth in the middle of the pool. Avoid sampling near return jets or skimmers. Once you have your reading, write it down. You’ll want to track changes as you adjust things.
There are two main chemicals used to bring pH down in a pool. Both work well. The right one depends on your situation.
This is the most commonly used option. It works fast and it’s widely available at hardware and pool supply stores. Muriatic acid is strong stuff though. You need to handle it carefully. Always wear gloves and eye protection. Don’t splash it around. Never add water to acid, only add acid to water. And always add it to the pool directly, not into the skimmer.
To use it:
For dosing, the general rule is about 100ml to 200ml of muriatic acid per 10,000 litres of pool water to lower pH by around 0.2 points. But always check the product instructions because concentrations vary.
This is a granular alternative to muriatic acid. It’s a bit safer to handle and easier to store. It’s sometimes sold as “pH reducer” or “pH minus” at pool shops.
To use it:
Dry acid works well but takes a little longer than muriatic acid to take effect.
Here’s something a lot of pool owners miss. If your total alkalinity is also high, lowering just the pH won’t last. It will bounce back up again in a day or two. Total alkalinity acts as a buffer. When it’s too high, it resists pH changes and keeps pushing pH upward. The ideal range for total alkalinity is between 80 and 120 ppm (parts per million).
If your total alkalinity is above 120 ppm, you need to lower that first before worrying too much about pH. The good news is that muriatic acid and dry acid both lower total alkalinity too. So by adding acid to bring pH down, you are also working on the alkalinity at the same time. It’s also worth noting that the type of surface finish in your pool can affect how quickly pH shifts. Certain pool finishes are more stable in aggressive water chemistry than others. Test both when you check your water. Treat them together and you will have much better results that actually stick.
Once you’ve added your chemical and let it circulate, wait at least 4 hours before retesting.
What to check:
What to avoid:
Testing habits:
High pH just needs a measured response. Test the water, pick the right chemical, adjust in small doses, and retest before anyone gets back in. The most important habit is regular testing. Catching a rising pH early means a small fix instead of a big one. And a well-maintained pool is more comfortable to swim in, easier to keep clean, and less likely to need costly repairs down the track. If something in your pool setup keeps throwing off your chemistry, like a circulation issue or ageing equipment, it may point to a deeper problem that a pool repair can sort out.
If you’re having ongoing issues with your pool water or thinking about a new build or renovation, the team at Epic Watershapes is happy to help.. Get in touch with us and we can talk through what your pool needs.
