All About pH!

how to test the pH of your swimming pool or hot tub

A balanced pH level in your hot tub / spa / swimming pool water is an essential starting point in maintaining water quality.  Check out our list of the most Frequently Asked Questions & our answers on:

“How To Manage Your Water pH.”


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pH Scale

What does the pH level measure?

pH is a measure of how acidic/basic water is. The pH range goes from 0 to 14, with 7 being neutral. A pH of less than 7 indicates acidity, whereas a pH of greater than 7 indicates a base. The pH of water is a very important measurement concerning the water quality of your hot tub / spa or swimming pool.

What should the pH level of my hot tub / spa / swimming pool water be?

The sweet spot you are aiming for is a pH level of 7.4-7.6


How do I measure the pH level of my hot tub / spa / swimming pool water?

You can do this using one of three methods:

Pool Lab Photometer Bluetooth Water Testing Kit
Check hot tub water pH

How Often should I check the pH level of my water?

This depends on several factors – in a commercial environment, at least daily.  In a home setting it depends on how balanced and stable your water chemistry is.  At least 2-3 times a week is a good guideline.  If this sounds wasteful or expensive in time and test strips, consider the effects of unbalanced water.

Is testing & maintaining pH levels in my hot tub / spa / swimming pool water expensive?

Consider the costs of poorly balanced water:

  1. Reduced equipment life. Unbalanced water will cause serious damage to the fixtures and fittings of your hot tub, swim spa or pool. The cost of replacing this equipment, especially things like pumps, heaters and salt systems, greatly outweighs the cost of maintaining proper water balance.  Damage caused by poor water chemistry is often obvious and the parts worn out by these means are unlikely to be covered by a manufacturer’s warranty.
  2. Water quality problems. The cost of properly maintaining your water is a fraction of the cost of remedying problems like green or cloudy water when they have developed. Fixing these water quality issues generally costs more than the balancing chemicals required to prevent them from occurring in the first place.
  3. Increased sanitizer usage. The effectiveness of sanitizers (chlorine & bromine) changes significantly with the pH of the water.

My water looks really clear – doesn’t that mean my pH levels are fine?

Without a pH test, there is no way of knowing.  Water that looks clear can sometimes be hiding serious problems.  Acidic water is capable of holding a lot of minerals in solution without the water turning cloudy. This might look good but isn’t good for you or your spa equipment.

Crystal Clear Hot Tub Water
Milky, cloudy, foaming hot tub water

My hot tub / spa / swimming pool water looks cloudy – does this mean my pH levels are unbalanced?

Cloudy water is often a sign that your pH levels are too high.  This would be the first thing to check if your water is cloudy, milky or foamy.  However cloudy hot tub water can also be caused by a number of other factors and these should all be checked and addressed as necessary.

What effect does pH have on the effectiveness of my sanitiser?

The disinfectant power of Chlorine is relative to the temperature and pH of the water. As pH increases, chlorine becomes less effective.  This means you have to add more chlorine to achieve the same results.  As pH decreases, the chlorine becomes more effective – but acidic water brings other undesirable issues (see Why is low pH in my hot tub / spa / swimming pool water a problem?)  So what we are aiming for is a balance – ideally around pH 7.4

pH   Effectiveness of Free Chlorine
6.0   97%
7.0    75%
7.2    63%
7.5    49%
7.6    39%
7.8    28%
8.0    3%

Why is low pH in my hot tub / spa / swimming pool water a problem?

PH levels below 7.2 could spell trouble for you and your spa. Acidic water makes it more likely that your chemical sanitizer will “burn out” quickly, leaving you exposed to potentially dangerous contaminants and bacteria.  Acidic water will corrode spa components such as headrests or jets. These can be expensive to replace.

Acidic water will potentially:

  • Corrode metal components
  • Damage pump seals and other spa components
  • Damage the acrylic shell
  • Burn out chlorine/bromine sanitiser so that you need to use more
  • Give bathers dry, itchy skin and stinging / burning eyes – human tears are pH 7.4
An image of 1kg pH Plus

My water pH is low, how do I increase the pH level of my hot tub / spa / swimming pool water?

The most common pH increaser, pH raiser, pH plus / pH + products available to treat low pH in hot tubs contain the active ingredient sodium bicarbonate.  Sodium bicarbonate is effective at increasing both pH and TA.

Why is high pH in my hot tub / spa / swimming pool water a problem?

When your pH level goes above 7.6, your spa water can be described as ‘basic’. This essentially means your spa water will be poorly sanitized.  Basic spa water can result in a flaky scale build up around your spa surfaces. The scale is due to a build-up of calcium caused by the high pH. Cloudy water is also another symptom of high pH levels.

Basic water will potentially cause:

  • Calcium build up
  • Damage pump seals and other spa components
  • Leave marks and staining on the acrylic shell
  • Give bathers dry, itchy skin and stinging / burning eyes – human tears are pH 7.4
  • Chlorine / bromine sanitiser becomes much less effective and the need to use more
  • Cloudy water and a gritty feel on hot tub surfaces
White Flakes in hot tub water
An Image of Relax pH Minus Granules 1.5kg

My water pH is high, how do I reduce the pH level of my hot tub / spa / swimming pool water?

pH decreaser, pH reducer or pH minus / pH– is a dry acid balancer, that you pre-dissolve in warm water then add to your hot tub / spa / swimming pool water.  The active ingredient in pH decreaser is usually sodium bisulfate.  Adding this will also lower Total Alkalinity, sometimes so significantly you’ll need to increase your TA back up a little afterward.

Can I Use Muriatic Acid to lower pH level?

You can, but keep in mind that although Muriatic acid provides an alternative way to decrease both pH and TA, it is an extremely caustic chemical.  You must store it safely and use protective glasses and chemical-resistant gloves and a great deal of caution when working with it – you really don’t want that burning your skin.

You won’t be able to just pour some in your spa, either. Muriatic acid will need to be diluted, added to your spa water, then aerated by running the spa jets. Finally, leave the spa to circulate overnight before retesting your water.

We don’t supply Muriatic Acid at Castle Hot Tubs.

Can I use Cyanuric Acid to lower pH level?

No.  Cyanuric acid technically is an ‘acid’ but it is not like muriatic acid.  It has little overall effect on pH, alkalinity or hardness and should not be used for the purpose of lowering pH levels.

Should I use Bromine or Chlorine sanitiser if my pH is unstable?

Bromine is slightly more effective in an unstable pH environment.  But this isn’t really a basis for choosing which sanitiser to use.  Achieving a balanced pH water is a necessity, whichever sanitiser you use.

How do I stabilise the pH level of my hot tub / spa / swimming pool water?

Adjusting the Total Alkalinity is likely to help.  The term technically refers to the ability of a solution to neutralize acids—or buffer them.  In your hot tub/spa or swimming pool water, the importance of measuring TA is only slightly different. TA acts as a buffer for the pH level in your water, helping to keep the pH level stable.

Total alkalinity is important to your water balance, the first step in your water care process should be measuring and adjusting TA before adding any other chemicals. The ideal range for TA is 125 parts per million (ppm) to 150 ppm.

When you adjust your alkalinity, add small doses, one at a time.  Allow the dose to circulate before testing again.  Only after your TA is in the optimal range should you move on to adjusting pH.  Achieving the right TA may get your pH in the target range.

An image of 1kg Relax Total Alkalinity Plus
Aquafinesse Spa Clean Tablet

I can’t get the pH level of my water balanced – should I “re-pHresh”?

If you find yourself chasing high and low pH in your hot tub / spa water, the easiest option might be to drain your spa and start over. This might not be such an attractive option if you’re operating a swimming pool.  If a drain and refresh is the way you want to go, the day before you drain, add some spa clean tablets and run your jets to clean out anything that could be affecting your water chemistry. After draining, clean the interior of your spa.  Before re-filling consider using an in-line pre-filter that can easily be attached to your hose, ensuring that your fill water is free from contaminants.

We hope you have found our guide to achieving balanced pH levels in your hot tub / spa or swimming pool useful.

Check back regularly as we add to our Water Quality FAQs!

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