Why do my test strips show a low chlorine reading?


Have you added chlorine to your spa pool only to find the chlorine level is low?


This article is for those using a Chlorine or Bromine spa sanitiser.

Chemicals used to eliminate microbes in water are administered by the APVMA in Australia and the labels on spa sanitisers are certified by the APVMA.

Although we have many customers reporting that they deviate from the dosing instructions on the sanitiser label, we cannot recommend that you deviate from what is stated on the label.




Should I use Test Strips?

Yes, but only to balance your spa water but not to check the sanitiser level. Do not use the test strips to monitor chlorine levels. Instead, you should always follow the dosing instructions on the sanitiser label.

Most spa pool sanitisers use a chemical stabiliser that prolongs the amount of time that the chlorine remains in the water before "burning off". 

Even with this stabiliser, test strips can show a low chlorine reading (Free-Chlorine on some test strips) very soon after adding sanitizer, even though the sanitiser level is adequate. This can lead to an overdose of spa sanitiser in the spa.

NOTE: An overdose of spa sanitiser can result in deterioration and failure of components including plastic parts, heaters, pumps and jets


If I don't use test strips, how do I know if my chlorine level is correct?

Instead of using test strips for the chlorine level, we recommend that you follow the certified dosing instructions on the back of the sanitiser label. 


What are the dosing instructions?

Dosing instructions state the quantity of spa sanitising chemical to use per litre of water for your spa.

For a spa pool, it is usually represented as grams of sanitiser per 1000 Litres of spa water.

You need to read the label on the back of your sanitiser to determine the correct amount for the sanitiser that you should be using.

As an example, many chlorine-based spa sanitisers state to use 6 grams per 1000 Litres per day.

In this example, if your spa is 1000 Litres then you would put in 6 grams of sanitiser per day. If it is 900 Litres you would add 5.4g per day.


What if I cannot dose my spa every day as the dosing instructions say?

If you cannot dose your spa each day, we recommend following the instructions on the label and use the recommended shock dose.

If you are away for a longer time, we suggest reducing the temperature of your spa and then using the shock dose as recommended on the container label.


If not for measuring chlorine, what are test strips used for then?

There are test strips with many different types of tests on a single strip. As an example, a 3-way Test strip might test for Free Chlorine, pH and Alkalinity

pH and Alkalinity make up the majority of water balancing and you need to ensure that your water is balanced or you can risk damaging your spa and voiding the warranty through corrosion. Furthermore, if your spa water is out of balance your spa sanitiser will not work as efficiently.



For more spa chemical help, or to buy spa chemicals in Australia visit Spa Store Australia or to buy Spa Chemicals in New Zealand visit Spa Store New Zealand.

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