Practical guide: how to analyse and control your pool water?

In this article, you'll find a practical guide explaining the parameters and frequency of measurements you need to take to analyse your pool water. Then we give you precise answers about the thresholds to be respected for each parameter in order to maintain water quality. Finally, we present the different measuring tools with their advantages and disadvantages.

What is ‘balanced’ swimming pool water?

The balance of water in a swimming pool depends on 3 key parameters: pH, TAC and TH. These 3 factors are closely linked. Water balance is essential to ensure water hygiene, bather comfort and equipment protection.

Parameters that influence water balance

• pH
• The TAC (total alkalimetric titre) or water alkalinity
• TH (hydrotimetric titre) or water hardness.

In order to maintain water balance, disinfection needs to be monitored.

The challenge is to maintain a balance between three different parameters: the acidity, alkalinity and hardness of the water.

All about balancing swimming pool water

Why should you regularly analyse your pool water?

Regular analysis of swimming pool water is essential to protect the health of bathers, guarantee crystal-clear water and ensure the longevity of equipment.

• Protect the health of bathers: detect any imbalances (pH too high or too low, lack of disinfectant, etc.) and prevent the proliferation of harmful micro-organisms.
• Maintain water quality: spot any problems with cloudy water, green water or algae growth early enough to take swift action.
• Protect the equipment: the wrong balance (water that is too acidic or too chalky) can damage the walls, the pump and the filtration system, which is why regular monitoring is so important.

How often should you analyse your pool water during the season?

The water in your pool is constantly changing. Several factors influence water quality. The frequency with which pool water is analysed and checked depends on factors such as the season, the number of bathers and the weather conditions. Depending on the weather, the temperature of the water, the environment around your pool and the number of bathers, the water can deteriorate. To maintain the quality of your pool water, it is essential to analyse it regularly.

• At least once a week during the season to check the major parameters (pH, disinfectant levels, temperature).
• Once a month for more in-depth measurements: hardness (TH) and alkalinity (TAC).
• Twice a year (or more depending on use) to check the level of stabiliser (cyanuric acid) in chlorine or salt pools.

During periods of heavy use or if the weather is particularly changeable (high heat, rain), it may be necessary to test the water more frequently to prevent any imbalance.

Water parameters to be measured at least once a week

In the high season, your pool water needs to be analyzed on a regular basis. This allows you to intervene quickly with the right treatment, so you can continue to enjoy your pool every day.

• The ideal pH of the water is different depending on your means of disinfection:
  • For chlorine disinfection, it is between 6.9 and 7.4
  • For bromine or salt disinfection, it is between 7.5 and 7.8
• The ORP / Redox determines the effectiveness of your disinfectant (bromine, chlorine).
  • For optimum disinfection of water at 25°C, ideal ORP measurements should be between 650 and 750mV. This is one of the parameters that varies most rapidly because it depends on pH and UV values.
• The water temperature must also be kept under control.
  • Pool water that's too warm reduces the effectiveness of chemicals, which can lead to algae growth.

Water parameters to be measured once a month

• TH measures water hardness. It is expressed in French degrees (°f). Ideally, it should be between 10°f and 20°f.
• Below 10°f, the water is too soft, leading to corrosion.
• Above 20°f, the water is too hard. The water then becomes cloudy and milky, and limescale deposits appear.  
• TAC determines the alkalinity of the water. It is an essential element in water balance, along with pH and TH (water hardness). TAC should be between 80 and 150 mg/litre or ppm. A good balance of alkalinity determines the buffering capacity of the water and has an impact on the stability of the pH and acidity of the water.

Water parameters to be tested twice a year

Stabiliser levels (cyanuric acid) is a parameter that should be tested (chlorine or salt pools). The ideal level is between 20 and 50 mg/L. Above this level, your water risks becoming over-stabilised. An overdose of chlorine makes it ineffective, leading to the proliferation of bacteria, algae and fungi.

How to carry out reliable analyses of your pool water?

Different pool water analysis tools

To test the various water parameters, you can choose between the manual method with test strips and electronic testers, or the automatic method with connected water analyzers.

To test pH, for example, you can opt for a chemical reaction strip, a ph-meter, which is a handheld probe, or a connected water analyzer. Please read our comparison of pH measurement tools.

Pool test strips

Test strips, which are the most affordable in terms of price (between 20 and 30 euros cents per test), give results that are more or less reliable and precise. In fact, reading the result is an interpretation of the color indicated. If your water needs chemical treatment, it will be difficult for you to know what dosage of product to add.

There are, however, test strip readers available. Once the test strip has been dipped in water, the required values are displayed digitally on the screen. This compensates for any misinterpretation of colors. It's an additional investment (approx. 100 euros) that can prevent many misinterpretations and, above all, over-consumption of chemical products.

There are specific strips for each disinfection method: chlorine, bromine, salt or active oxygen. Depending on the brand and the product, the products can analyse from 4 to 7 parameters. To obtain reliable results, store them at room temperature, close the cap tightly and do not exceed the expiry date.

Pool electronic testers

Electronic testers or probes are much more reliable, but it's best to avoid the low-priced gadgets. These devices allow you to read a very precise digital result. However, they need to be calibrated regularly (depending on the model). You can ask your specialist for advice, as he or she is familiar with specialist pool brands.

Finally, some testers analyze only one parameter (pH or ORP), while others allow you to test several water parameters, which is more economical and, above all, more practical!

Connected water analyzers

For the past five years, the market for connected sensors has been booming. The key benefit of these devices is their ease of use, since the main parameters of your pool water are measured automatically every day, several times a day. Some connected sensors like ICO Pool give you access to the results of your measurements on your smartphone, along with chemical treatment recommendations with the right dosage. Thanks to ICO, pool maintenance tips, such as filtration or winterization, save users a lot of chemicals and time! Read the comparative report on connected probes.

How to do a reliable water testing

Before comparing the various pool analysis tools, it's important to remember that whatever the method used, it's important to carry out the analyses under the right conditions to obtain reliable results.

Whether you use a colorimetric strip or an electronic tester, here's how to do your test:

• Where to test? Perform your test in the middle of your pool, and test the water as far away from the edge as possible. In fact, water on steps or a submerged beach is less representative than water in the middle of the pool.
• Taking a water sample: to use this system correctly, you first need to take a water sample 40 cm below the surface. This is because the water at the water line is warmer and has a different composition. Of course, your container must be very clean, with no trace of chemicals that could pollute the result. Immerse your test strip in the water for 5 to 10 seconds before reading the result.
• Immerse a test strip: immerse the test strip in water (always favouring an area in the middle of the pool) and read the result immediately. Depending on the brand used, the result should be read between 5 and 15 seconds after immersion. The color continues to vary for several minutes, so it's important to read at the right moment.
• Using an electronic tester: Place your tester under the surface of the water (3cm minimum) then wait 5 to 10 seconds before raising your tester to read the result.
• When to do a water test: it's best to do your test in the morning or evening, but always at the same time! This allows you to compare your results from one test to the next.

Water analysis and pool maintenance, the right combination for crystal-clear water

To keep your pool water balanced, good pool maintenance is just as essential as regular water analysis. Maintenance must be regular (at least weekly in high season) and thorough: from cleaning the walls and water line to cleaning or replacing filters and pre-filters. On average, 30 minutes of maintenance every week is enough to keep your water crystal-clear. All you have to do is enjoy your bathing!