A complete guide to pool water testing

Understanding and managing your pool chemistry is a key requirement for operating a swimming pool safely, whether you have a private pool at home or offer swimming facilities to guests at a holiday park, gym or spa. Accurately testing the water in your pool with the right testing equipment provides the information you need to dose your water, ensuring it is safe and hygienic. We cover everything you need to know about pool water testing in our complete guide. Read on to learn more:

Why should you test the water in your pool?

Testing your water quality in pools, hot tubs and any other water that requires sanitation is a part of maintaining health and safety. Pool water that is consistently monitored can be dosed appropriately with swimming pool chemicals in a safe and timely manner. 

Sanitation that goes unchecked can be too low, resulting in the risk of diseases such as Legionnaires’ disease due to pathogens being able to survive in the water. Water chemistry that is too strong can cause harm to bathers, including skin and eye irritation.

In addition to the risks to bathers and swimmers, testing the water in swimming pools also helps to maintain the condition of the pool. Measuring certain parameters such as calcium hardness can allow changes to be made to the water chemistry to prevent scaling on vital parts of the pools such as heaters, pumps, jets and pipework, improving the longevity of parts in and around the pool area.

What parameters should you measure in swimming pools?

pH

pH is a measurement of how acidic or alkaline the water is, on a scale from 0 to 14. pH is the first step in pool water testing as this parameter affects all other parameters, altering the level of sanitation of the water in the pool. pH is also altered by the temperature of the water, making it important to take measurements at the correct temperature level or use a digital tester with temperature compensation built-in. Learn more about why pH testing is important here.

Chlorine

Chlorine is the most commonly used sanitiser for pools and hot tubs. This pool chemical eliminates bacteria, pathogens and contaminants, effectively making the pool water safe for use by swimmers. Monitoring chlorine is vital to achieve the correct level of sanitation, reducing the risk of illness while preventing overdosing, which may cause skin irritations and other health issues. 

Total Alkalinity

Total alkalinity is a buffer in pool water chemistry, preventing significant swings in pH that can cause changes in the sanitation of the pool. As a way to maintain balance within pool water day to day, total alkalinity is an important measurement. Testing this parameter helps to prevent issues relating to scaling and corrosion.

Calcium Hardness

Calcium hardness, which is also referred to as total hardness, is another key measurement for all swimming pools. Ensuring calcium hardness stays below a certain level helps to prevent scaling, which can occur to many working parts of the pool such as the heaters, pumps and jets, ultimately causing faster degradation and failure. 

Total Dissolved Solids

In pools with a higher volume of swimmers, such as those in gyms, hotels and holiday parks, measuring total dissolved solids is an important additional parameter. Testing TDS provides insight into the dissolved compounds in the water, which can be introduced by bathers. This number should be as low as possible for health and safety purposes.

Cyanuric Acid

Cyanuric acid is a common additive to swimming pools and hot tubs that are outdoors. Ultraviolet rays from the sun cause chlorine to degrade, reducing its effectiveness. Cyanuric acid protects from this degradation, keeping pools sanitary, but it can also negatively impact sanitation if the level of this chemical becomes too high. Careful testing for outdoor pools ensures you’re in the correct range to keep the water safe.

To learn more about the correct ranges for pH, chlorine and other vital water quality parameters, see our article here.

How often should you test swimming pool water?

How often you test the water in your pool depends on a range of factors. For example, outdoor pools may need more frequent monitoring as debris, rainwater and other organic matter fall into the water, potentially causing significant swings in pH. Commercial pools with a high bather count will also need to increase testing and dose accordingly. Typically, the water in pools should be tested at least once per week for all of the most significant parameters - pH, Chlorine and Total Alkalinity.

In higher-use periods, such as in the summer, it’s important to increase testing in line with the volume of pool usage. If a pool is closed down or covered for winter, performing a full set of tests before dosing the water for the new season is key to saving money on chemicals and ensuring your water balance is in the right place.

If you’re unsure what your testing schedule should look like, our Pool Line ambassadors would be happy to provide guidance and suggest the best digital pool testers, photometers or automatic controllers for your requirements. Contact them directly now.

How do you test swimming pool water?

There is a wide range of different options to test pool water. These include:

Test strips and kits

Testing strips for pools and chemical testing kits are a cost-effective option for pool water measurement. However, these options require you to determine the results of testing with your own personal perception. This lack of precise accuracy can result in pool water being under or over-dosed, which can be costly in remediation or additional pool chemicals.

Digital testers

Digital testers are an accurate, pocket-sized method for the measurement of all key pool parameters. An electronic tester can take a reading directly from the pool water with a dip-and-test method or can use a small sample of pool water to take a precise measurement, depending on the instrument. 

These simple testers are portable and easy to use on-site and take up little room for storage. Hanna’s HI-981074 pocket tester is an example of a practical digital pool pH tester that makes measurement as straightforward as possible.

Photometers

Photometers are a highly accurate and practical way to measure many of the most important pool parameters with one instrument. Multiparameter pool photometers use a small sample of water taken from the pool in a vial that is inserted into the meter with the required reagents. 

The results of the testing are shown on the screen, allowing you to make precise choices for dosing your pool water. The HI-971044 photometer is an example of these advanced pool testers, covering all important pool parameters.

Automated dosers

Automated dosers are a fully automatic solution for pools and hot tubs that remove the need to test hands-on entirely. Instead, the fixed dosing system measures the water at regular intervals and doses chlorine and pH directly to achieve the ideal range that is defined by the user or a pool engineer. 

These meters can also be connected to the cloud, allowing you to monitor the condition of the pool water directly from a smartphone. The BL-132-20 pool controller is an ideal option for peace of mind in pool care, automating dosing and measurement in one. Learn more about automatic dosing for pools here.

Testing for hot tubs

Like swimming pools, hot tubs require careful monitoring and water balancing to be safe and hygienic for bathers. Businesses with hot tubs can use digital testers to adhere to HSG282 legislation. Hanna’s range of testers, photometers and automatic dosers are also designed to be used in hot tubs and spas. Learn more about how to test the water in hot tubs here.

How to take an accurate sample for testing

The ideal location to take a sample from your pool is as close to the centre as possible. Swimming pools have a large volume of water, which means there can be inconsistencies in water chemistry in different locations, such as closer to heaters or near the inlet for the pool. You may also choose to take several measurements to get an idea of water chemistry in multiple areas, which is an easy process with a dip-and-test digital pool tester.

What can cause inaccurate readings when testing pool water quality?

There are a few factors that can lead to inaccuracy in your test results. These include:

Taking samples from the wrong area

If you take your water samples or directly measure the water too close to inlets or near a dosing system, if you have one, this may lead to your pool testing results being inaccurate. It is best to take your measurements near the middle of the pool and in roughly the same place each time. This helps to ensure accuracy in testing.

Testing an old water sample

If you are measuring your pool water using a photometer or testing kit, you will need to remove a sample from the pool itself for testing. It’s important that you test soon after removing the sample while also keeping in mind any temperature requirements for your specific instrument or process. Water that is left uncovered for a significant amount of time may have different readings to water taken fresh from the pool.

Not cleaning your tester

Build-up of chemicals inside testing vials or on the electrodes of digital testers for pools can cause inconsistency in results. Following the instructions for cleaning your instrumentation, usually by rinsing with deionised or distilled water, can prevent this build-up from occurring and improve the accuracy of your testing. Hanna’s testers and photometers include maintenance and cleaning directions as part of the manuals included in the box.

Personal perception of results

If you are using test strips or a chemical test kit, you are relying on your perception of results to make decisions about your pool chemistry. While digital testers display precise results, test strips for pools usually cover a range, which increases the risk of inaccurately reading the outcome of testing. Reading the results of your test wrong can be a costly problem, requiring the use of more pool chemicals or remediation to reduce sanitation.

Buy pool testing equipment from Hanna

Hanna’s Pool Line range includes a full selection of accurate digital testers, comprehensive pool photometers and fully automated pool systems for dosing and monitoring vital sanitation parameters. 

Shop our range of testers for swimming pools and hot tubs online today, or get in touch with our pool ambassadors to discuss your specific requirements. Call us on 01525 850 855 or email us at sales@hannainstruments.co.uk.