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What are DPD Tablets?

What are DPD tablets you ask?

Well they are used to measure chlorine levels, which is the most used way of disinfecting the water. These tablets are most commonly used for swimming pools, drinking water and industrial process water.

When you use the chlorine to disinfect the water, the goal is to kill any germs. So you need to leave a small amount of active (Free) chlorine in the water, this is known as "residual chlorine" which is important as there will be chlorine available to help disinfect any further contamination of the water. Combined (Total) chlorine is where the sum of the free chlorine available in the water which is used to disinfect future germs and the chlorine that has been used and bound jointly with the pathogenic molecules.

 It is of vital importance to work out the right amount of chlorine that needs to be added and too much is a negative to health and waste money and then too little chlorine can result in their being a high level of the disease that will cause the pathogens. How much Chlorine you need can be determined by deducting the residual from the amount of chlorine that has been added. 


There are 4 different DPD tablets that are available which are 

  • DPD 1: This will measure free chlorine, which is the cholrine that is in the pool to kill any bacteria.
  • DPD 2: This is used to measure Monochloramine. DPD 2 are a less successful and used way of disinfectant than chlorine 
  • DPD 3: This will measure combind chlorine, so when you add dpd 3 to the same sample as dpd 1, you will be able to work out the total chlorine. 
  • DPD 4: This is used to measure total chlorine only. 


These tablets can be reliably used to measure chlorine levels from 0.001 mg/l t0 10mg/l. So, when a sample that has a chlorine level of more than 10 the colour will be beached out of the tablet, there will be a show of a pink colour. Then after the colour as gone it will return to its original colour. You can use Dilutions to help determine high range of chlorine levels.  

How will i know if my tablets aren't working?

You will know if the tablet has deteriorated as if the tablet is not white but has turned a grey/brownish or purple colour. You must avoid using deteriorated tablets as they will give false results. 



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