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DPD Method For Ozone

What is Ozone? 

This is a toxic gas and conesquently in larger installtions, must been removed from the water before it is returned to the pool after treatment.

But in spa pools, small amounts are generated to combat the oxidisable products which are produced-combined chlorines etc. This means that ozone rarely get back into the spa itself. 

Concentration of ozone in the atmosphere above the spa pool water should not exceed 0.1ppm.


To test for ozone in water you would need to use the DPD method.

You can test for ozone in the absence and presence of residual chlorine or bromine .


Ozone in the Absensce of residual chlroine or bromine 

-rinse a cell with sample and leave empty

-add either(1 dpd No.1 tablet and 1 DPD No.3 tablet), or ( 1 DPD no.4 tablet) and crush with a clean stiring rod.

-add the water to the 10ml mark and mix gently with the stirring rod to dissolve the tablets.

-Match the colour produced either colorimetrically or photometrically and record the redaing as residual ozone in mg/l - call this A 


 Ozone in the Presence of residual chlroine or bromine

The Above procedure is followed and the reading now corresponds to ozone plus total residual chlorine or bromine

the second procedure is as follows

-Rinse a second cell thoughly than fill to the 10ml mark

-Add 1 DPD glycine tablet, crush and mix to dissolve with the clean striring rod.

-Rinse second cell with sample and leave empty

-Add either (1 DPD no.1 and 1 DPD No.3 tablet), or ( 1 DPD No.4 tablet) and crush with striring rod.

-Add this cell to the solution in the first cell and mix thoroughly to dissolve the tablets

-Match the colour produced either colorimetrically or photometrically and record the redaing as total chlorine or bromine in terms of ozone in mg/l in mg/l - call this B


To obtain the ozone concentration subtract reading B from reading A.

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