DPD powder

[Poolidiot]

No one else has run into this?

[waterbear]

If you OTO test turned dark orange then it means that you have high chlorine levels. DPD will bleach out at high chlorine levels making you think you have NO chlorine in the pool. Have you tried adding more than one scoop of DPD powder...sometimes that will work. Taylor recommends adding the DPD powder by the scoop until the pink color holds.

Also it is possible that you have no FC in the pool, only CC. When you add the third reagent to test for CC does it turn pink then? (even for a second?)

[waterbear]

I seem to remember reading on the old forum that if the DPD powder is light grey it is still ok to use but if it has turned dark it is no good. This is because it has become completely oxidized and had turned into a dye. DPD is an aniline dye precursor. When DPD oxidizes (from oxygen in the air, usually in the presence of moisture) it will turn dark. As an analogy, think of a bottle of hair dye. It starts out as almost colorless and when it is mixed with the peroxide it turns dark, hopefully after it has penetrated the hair. (I use this analogy because DPD IS one of the dye precursors used in permenant hair dye). It is still usable as long as it is not completely oxidized. You just might need to add more to develop the pink color. In this case chlorine is the oxidizing agent that is developing the dye (Wurster's dye which has a pink color). Just like a bottle of hair dye is usable as long as it has only darkened slightly and not turned completely dark. (I have been a licensed Barber and licensed Cosmetologists for 30 years now and have taught both professions in the past so I have some knowledge of this.)

[Poolidiot]

The powder is a light grey, I dont think it is bleaching it out, I showed around 2 ppm with the oto test, then I took water sample from my pool and wanted to see if my dpd powder was working so i added str8 bleach to the sample just to get a reading, so it might have bleached out the powder that time but before I did that my oto showed 2 ppm and powder showed none and then when i added str8 bleach my dpd still showewd 0 but oto turned burnt orange , If that makes since.

[Watermom]

DPD powder does go bad. You may just need to order some new.

[waterbear]

Then it probably is bad. How many scoops did you add?

[Poolidiot]

I added 1 scoop the first time then 2 the 2nd time...it is not even a year old

[let_her_flicker]

I have ordered DPD powder for my PS233 kit from Ben for about 5 years now. Last year I did a comparison. I tested the new and old powder side by side. New powder was white and the old powder was darker, had some clumps in it, but it was not black. I crushed the clumps with the spoon.

Both measured exactly the same. That was my experience. I did not keep checking the powders until they did not measure the same. I do know that the darker powder still did its job, but at some point I am sure there would be a difference. Time wise, the darker powder I check was 14 months old, kept inside, and was never wet.

Hope this helps.

Harry