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Bio-Lab presently distributes three types of DPD Tablets. They are DPD #1, DPD #3, and DPD #4.

 

DPD #1 is very sensitive to moisture and air. Under ideal conditions the tablets are good indefinitely. Tablets are sealed individually in metal foil for their protection. Upon degradation, the tablet first exhibits brown speckles. Next, the tablet turns entirely brown, and finally disintegrates into powder. DPD #1 tablets are made of reagent, buffer, and a dispersing aid. The dispersing aid is not water soluble. Thus, the resulting pink test solution is slightly turbid. DPD #1 will test for free available chlorine, bromine and bromamines. It will not test for chloramines (combined chlorine).

 

DPD #4 is a mixture of DPD #3, buffer, and DPD #1. This mixture is more sensitive to degradation than DPD #1. The tablets do not contain a dispersant. They give a clear test solution. The DPD #3 tablet is sensitive to total active chlorine, bromine, iodine and other oxidizers, such as OxySheen and hydrogen peroxide. To avoid low test results, the DPD #4 tablet should be crushed in the test chamber before the water sample is added.

 

DPD #3 is a very stable chemical.

 

Very high levels of chlorine can bleach out and destroy DPD #1 indicator. Very high levels of chlorine will react with the DPD #3 tablet to produce a brown or yellow colour. Thus, if you do not get a reading for chlorine on the DPD #1 tablet, you can use the DPD #3 tablet to determine if there is no chlorine at all or if chlorine levels are actually so high they are bleaching out the DPD #1 indicator.

 

CAUTION: Oxidizers other than chlorine (OxySheen and other products containing peroxymonopersulfate) will react with DPD #3. In the presence of a DPD #1 tablet and a DPD #3 tablet they will give a false reading for chloramines. When only the DPD #3 tablet is used, these other oxidizers will produce the same yellow to brown colour produced by chlorine. Neither the DPD #3 or DPD #4 tablets can be used to measure chloramines or combined chlorine in pools shocking with a non-chlorine shock treatment (peroxymonopersulfate). Peroxymonopersulfates very slowly react with DPD #1 and do not interfere with the DPD test for free available chlorine.

 

The above information is supplied by Bio-Lab and represents its best interpretation of available technical information at the time of preparation. The sole purpose is to supply factual information to Bio-Lab customers. It is not to be taken out of context nor used as support for any other claim not made herein.