Swimming Pool & Spa Water Testing

A Guide To Water Testing Your Pool

There can be quite a lot that goes into making sure your home pool is looking and feeling great year-round. However, one of the most important aspects of pool care has to be testing water chemistry, such as the chlorine, pH and total alkalinity levels of your pool!

There are many ways you can go about this, but the most important thing is ensuring that you’re getting accurate results from your tests. Here, we take a look at the whole process and what you should be looking out for when water testing your home pool.

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Why Water Test Your Pool?

Ultimately, the reason you should frequently be testing the water quality of your pool is for health and safety. You must ensure your pool’s water is safe to swim in for prolonged periods – too many or too few chemicals can both compromise the water’s hygiene and safety.

Another reason you should be testing your water’s quality is for the longevity of the pool. Again, having a chemical solution that is too strong or too weak can have detrimental effects of various parts of the swimming pool, including pumps, filters and linings.

What to Look for in a Swimming Pool Water Test

As a general rule, you are testing the water for three different things:

Chlorine level.
pH Level.
Total Alkalinity.
Depending on your pool and the chemicals used, you may also need to check for other chemicals, including calcium hardness, acid strength and dissolved solids. However, the main things you should be testing for are the three mentioned above.

An inflatable football in a swimming pool while it’s raining

How Frequently Should I Test My Swimming Pool Water?

Different chemicals need to be tested at different frequencies, based on how much they can fluctuate and their importance to the overall health of the pool. The main three tests as mentioned above – chlorine, pH and alkalinity – should be tested at least once a week during use, with the other checks occurring monthly.

At Alliance UK, we always recommend people conduct these tests daily, to ensure the chemicals in the water are at a safe level.

All necessary tests should be made when opening your pool for the first time after a prolonged closure, such as during the winter. Furthermore, all tests should be completed before closing your pool.

As all swimming pools are different, the test frequency should be adjusted to suit your needs. Speak to a professional who might recommend another particular test that your pool should take more frequently. Also, when the pool is in frequent use, such as during the summer, it is recommended that these tests happen more regularly.

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How Do I Test My Swimming Pool Water?

The most common method of testing water quality is through testing strips. Testing strips feature squares that change colour depending on the strength of certain chemicals in the water.

Another option for testing water quality comes in the form of liquid or tablet solutions. These involve taking a sample of the water and mixing it with provided solutions or dissolving tablets. Similar to testing strips, the water sample then changes colour to show how much of a particular chemical is present.

There are some digital testing kits now available, which use electrodes to detect chemicals in the water, although this is often an expensive option for home pools. You can also take a water sample to a swimming pool supplier who should be able to provide an accurate reading. This approach can be useful if you feel that you are getting inaccurate readings or are opening your pool after an extended closure.

Which Water Test is Best?

It’s worth noting that, so long as you buy your testing kit from a reputable supplier, all variations described above should provide an accurate and safe reading if the instructions are followed.

Many people opt for testing strips because they are the most simple to use and least expensive. Solution or tablet-based options can take longer but can also produce more accurate results, particularly for large pools as it relies on you taking an accurate sample.

How to Take an Accurate Water Sample

A swimming pool is a large body of water and, as a result, the chemical makeup can be different in certain locations. For example, evaporation and other influences can make the water at the surface of the pool have a slightly different composition to that at the bottom.

For the most accurate result, it’s recommended that you take a sample from the centre of your pool, preferably close to the surface.

Rippling swimming pool water

What Levels to Look For When Testing Swimming Pool Water

While there can be some slight discrepancies in terms of chemical levels, there are general guidelines in which you should look to keep your pool. All of the recommended levels should be made apparent in your swimming pool testing kit.

Chlorine
Chlorine levels should read between one and three parts per million (ppm). If your chlorine is too low, increasing the dosage is straightforward. If it is really low, you may require a shock treatment.

If your chlorine levels are too high, then removing the dosage – often administered through a pool floater – and allowing it to sit will naturally lower the chlorine levels.

pH
Your pH levels should often read somewhere between 7.2 and 7.6. Generally, 7.4 is seen as the sweet spot.

pH is a relatively easy thing to increase and decrease, so long as you have the correct chemicals. There are many pH increasers and decreasers available.

It is worth noting that pH readings can be influenced by other chemicals, such as if there’s too much chlorine or not the right alkalinity. Therefore, it’s often recommended that you test the pH balance last, once the others have been confirmed.

Alkalinity
You pool water’s total alkalinity should read between 80 and 120 ppm.

As with pH, raising or lowering alkalinity depending on the results is straightforward if you have the right chemicals available. Note that alkalinity and pH are linked, so adjusting the alkalinity may also impact the pH level.

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Common Mistakes When Testing Water

If you have followed the instructions but are unsure with your reading, here are some common errors which can skew results.

No Chemical Reading
If you are using test strips and getting no reading back from the water, this is often a result of chlorine levels. Sometimes, having a chlorine level that is too high can cause a bleaching effect on the strips, whereas having no chlorine can also impact other results.

If you believe you may have added too much chlorine, mix your water 50/50 with tap water to see if another test strip then produces a result. If it does, then you are likely to have too much chlorine.

Purple pH Reading
The majority of pH testers will use a scale from yellow to orange. If you believe that you have the right pH level, but your tests return purple, this can also be a result of too much chlorine in the pool.

Interference with Tablets
If using a testing kit that involves dissolving tablets, ensure that you do not make contact with them. Handling the exposed tablet can cause inaccuracies with the final results.

Time Between Sample and Result
One of the biggest reasons for inaccurate water testing results, besides where you take the water sample from, is time. Leaving your water sample exposed for too long before testing it can lead to inaccurate results.

Similarly, when using a solution-based test, leaving the final solution for too long can lead to changes in the colour, giving inaccurate readings. Thankfully, simply performing the test as instructed without unintended breaks will remove this issue.

Clean Testing Kits
A problem that can occur over time with the solution and tablet-based tests is the contamination of the testing tube, which can falsely change the final results.

When performing a new test, you should not rinse out the tube with clean water. Instead, rinse the testing tube with water from the pool. That way, all water left inside will have a similar chemical makeup to your testing sample.

For any specific problems with your pool water, check out our water treatment troubleshooter.

A woman flinging her hair to create a water pattern in a swimming pool

We hope that this guide will give you the confidence and knowledge to test your swimming pool accurately. Remember, all pools are slightly different, as are all tests, so follow the advice given to you by the products and your suppliers.

If you’re after some new swimming pool chlorine tablets, pH adjusters, testing kits or anything else, why not browse our complete range? If you have any more questions about anything we’ve mentioned here, feel free to get in contact with our experienced local team!