Pool pH: How to Lower High pH and Alkalinity

Cloudy water and stinging eyes usually have a simple fix

If your water has turned a little dull, or swimmers are coming out rubbing their eyes, the cause is often easier to sort than you might fear. In many cases it comes down to pool pH sitting too high, with total alkalinity drifting up alongside it.

The good news is that you don’t need a chemistry degree to put it right. You need a reliable test kit, a little patience and a clear plan. That’s what this guide is here for.

We’ll explain what pH and alkalinity actually are, why they tend to climb, and how to bring them back down safely. We’ll also share the simple routine we recommend to owners, so small wobbles never turn into big problems.

Who this guide is for

It’s written for anyone who looks after their own pool, whether you’ve just had one installed or you’ve been swimming for years. If you’d rather hand the testing over to someone else, that’s fine too. We cover servicing and aftercare, and we’re always happy to help.

Pool pH and alkalinity work together as a team

These two readings are closely linked, so it helps to understand both before you reach for any chemicals.

What pH measures

pH is a scale that shows how acidic or alkaline your water is. It runs from 0 to 14. Seven is neutral. Anything below 7 is acidic, and anything above 7 is alkaline (sometimes called basic).

For a swimming pool, most experts recommend keeping pH between about 7.2 and 7.6. That range is comfortable for swimmers and lets your chlorine do its job properly. It’s also close to the natural pH of our eyes, which is why balanced water feels so gentle.

What total alkalinity measures

Total alkalinity is a little different. It measures the amount of dissolved alkaline substances in the water, mostly bicarbonates. It’s measured in parts per million, or ppm.

The widely used target is roughly 80 to 120 ppm. Some pool types, sanitising systems and installers work to slightly different figures, so always check the guidance for your own pool.

How they affect each other

Think of alkalinity as a shock absorber for your pH. It soaks up small changes and stops the pH from bouncing around every time it rains or someone jumps in.

That’s helpful when alkalinity sits in the right range. When it runs too high, though, it acts like an anchor that keeps dragging pH upwards. You bring the pH down, and a day or two later it’s crept straight back up. This is why we usually tackle alkalinity first.

High pH causes more trouble than you might expect

A reading of 7.9 or 8.0 might not sound far from the target. Yet it makes a real difference to how your pool looks and feels. Keeping your pool pH in range protects both your water and the people swimming in it.

• Weaker chlorine. Chlorine works best in slightly lower pH. At around 7.5, roughly half of it is in its strong, fast-acting form. At 8.0, that falls to around a fifth. So you can have plenty of chlorine in the water and still struggle to keep it clean.
• Cloudy water. High pH encourages dissolved minerals to come out of the water, giving it a milky or hazy look.
• Scale. Those same minerals can settle as a crusty white or grey build-up on surfaces, tile lines, heaters and pipework.
• Irritated eyes and skin. Swimmers may notice stinging eyes, dry skin or itchy patches.
• Greater risk of algae. Because your chlorine is working harder, algae has a better chance to take hold. Our guide to dealing with pool algae explains more.

Several everyday things push pH and alkalinity upwards

It’s completely normal for pH to rise over time. Here are the most common reasons we see.

Your fill water

Much of the South East, including Surrey, has hard water. Tap water here often arrives with high alkalinity and a fairly high pH. Every time you top up after evaporation or backwashing, you add a little more.

Your sanitiser

Some types of chlorine, such as liquid chlorine and chlorine granules made with calcium, are naturally alkaline. Salt chlorinators also tend to push pH up as they work. None of this means you’re doing anything wrong. It just means you’ll need to bring pH down now and then.

Splashing and water features

Anything that stirs the surface lets carbon dioxide escape from the water. As it escapes, pH rises. Waterfalls, fountains, spa jets and lively swimmers all play a part. Warmer water adds to the effect, so heated pools can see more drift. If you’re thinking about warming your pool, our swimming pool heating guide is a handy read.

Over-correcting

Sometimes alkalinity rises because too much alkalinity increaser was added in the past. It’s an easy mistake to make, and a good reason to add small doses and test in between.

Testing your pool pH takes just a few minutes

You can’t fix what you can’t measure, so good testing is the foundation of everything else.

Choosing a test kit

• Test strips are quick and simple. They’re great for a fast check, though colours can be tricky to read.
• Liquid drop kits are more accurate and still easy to use once you’ve done it a couple of times.
• Digital testers give a clear number on a screen, which takes the guesswork out of reading colours.

Whatever you use, keep it out of direct sunlight and replace reagents and strips before they expire.

How to take a good sample

1. Take your sample from elbow depth, roughly 45 cm below the surface.
2. Choose a spot away from the return jets and any skimmers.
3. Test with the pump running, ideally before anyone swims.
4. Test total alkalinity first, then pH.
5. Write down your results so you can spot patterns.

How often to test

During the swimming season, we suggest checking pH two or three times a week and alkalinity once a week. Test more often after heavy use, a big top-up or a spell of hot weather.

Lower alkalinity first, then fine tune your pool pH

Once you know your readings, you can decide what to do. If alkalinity is above your target, start there. If alkalinity is fine and only pH is high, skip straight to lowering pH.

Stay safe before you start

Pool chemicals are safe when handled properly, but they deserve respect. Please follow these rules every time.

• Wear chemical-resistant gloves and eye protection.
• Always add chemical to water, never water to chemical.
• Never mix different chemicals together, even in the bucket or on the scoop.
• Keep swimmers out of the pool until the water has circulated and your retest shows it’s balanced.
• Store chemicals in their original containers, somewhere cool, dry and well ventilated, and well away from children and pets.

Choosing your product

There are two common options for lowering both readings.

• pH reducer, also called dry acid. This is usually sodium bisulfate in granular form. It’s the easier and gentler choice for most home owners.
• Hydrochloric acid. Sometimes called muriatic acid, it’s stronger and works quickly. It gives off harsh fumes and can cause serious burns, so it must be diluted and handled with great care. If you’re at all unsure, stick with dry acid or ask us to help.

Always follow the product label for dosing. Labels tell you how much to use for your pool’s volume.

Step by step: lowering high alkalinity

1. Work out your pool’s volume in litres, so you can follow the label accurately.
2. Calculate the dose for the drop you need, then use only part of it. Around half is a sensible first step.
3. If using dry acid, pre-dissolve it in a clean plastic bucket of pool water. If using liquid acid, dilute it by adding the acid slowly to a bucket of water.
4. With the pump running, pour the mixture slowly and low into the deep end, away from skimmers, steps and fittings.
5. Let the water circulate for several hours.
6. Retest alkalinity and pH.
7. Repeat in stages until alkalinity reaches your target.

Adding acid lowers pH at the same time as alkalinity, and pH will often drop below 7.2 during this process. Don’t panic. That’s expected.

Bringing pH back up with aeration

This is the clever part. Aeration raises pH without raising alkalinity. So once alkalinity is where you want it, you can lift pH gently using air.

• Point your return jets upwards so they break the surface.
• Run any water features, fountains or spa jets.
• Use an air blower if your pool has one.

Keep aerating and retesting until pH settles back between 7.2 and 7.6.

Step by step: lowering high pH on its own

If alkalinity is already in range, the process is simpler.

1. Measure a small dose of pH reducer, following the label.
2. Pre-dissolve or dilute it as above.
3. With the pump running, add it slowly around the edge of the pool, near the return jets, so it spreads evenly.
4. Wait several hours for it to mix, then retest.
5. Add more in small amounts only if needed.

Slow and steady wins here. Big doses can overshoot, and then you’re chasing the problem in the opposite direction.

A simple routine keeps your water balanced

Once your water is back in range, a steady routine makes life far easier. Most owners find their pool pH needs a small nudge every week or two in summer, and far less in the cooler months. Here’s what we recommend to our own customers.

• Test on a schedule. Pick set days and stick to them. Little and often beats big corrections.
• Keep a log. A notebook or phone note helps you see if pH creeps up after rain, heavy use or top-ups.
• Correct early. A small adjustment at 7.7 is far easier than a large one at 8.2.
• Use a cover. A cover reduces evaporation, which means fewer top-ups with hard tap water. It also helps with your pool running costs.
• Clean regularly. Skim, brush and keep filters clean so your chemicals aren’t fighting debris.
• Get a service. A professional check each season can catch issues before they build.

Our one-piece pools are designed to be low maintenance, with smooth surfaces that are easy to keep clean. You can see our range to find out more. Even so, every pool benefits from regular testing, and we’re always glad to show owners how to build it into their week. If you’re weighing up your options, our guide to saltwater pools is worth a look.

Water balance questions we get asked a lot

How long does it take to lower pool pH?

A single small dose usually shows a change within a few hours. Bringing high alkalinity down can take a few days, because it’s best done gently in stages.

Can I swim straight after adding acid?

It’s best to wait. Let the water circulate for several hours, retest, and only swim once your readings are back in range.

Why does my pH keep rising?

The usual culprit is high alkalinity pulling it back up. Hard fill water, some sanitisers and lots of splashing can also play a part.

Is it better to lower pH or alkalinity first?

If both are high, lower alkalinity first. Then use aeration to bring pH back up to the right level.

Can pH be too low?

Yes. Low pH can make water corrosive, which may damage equipment and irritate swimmers. Aim to keep it within the target range rather than as low as possible.

Can someone else look after this for me?

Of course. We offer servicing and aftercare, and we can also help you set up a simple testing routine you’re comfortable with.

Help with your pool pH is only a phone call away

Keeping pH and alkalinity in balance becomes second nature quite quickly. With the right kit and a few good habits, you’ll spend far more time enjoying your pool than worrying about it.

If you’d like a hand, whether that’s a one-off check or regular aftercare, our friendly team is here for you.

Call us on 01483 323 676 or email hello@hilifepools.co.uk for a friendly, no-pressure chat, or get in touch online and we’ll come back to you.