Does R-0870 DPD Powder ever expire?

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DangerBoy

DangerBoy

Well-known member
Oct 4, 2018
167
Calgary/Alberta
Something weird is going on with my free chlorine testing. I've added more than enough 10.3% chlorine to bring my hot tub water to at least 6 ppm FC yet when I add the 2 dippers of DPD powder to the sample, it only slowly turns faint pink and according to the test, my FC level is only at about 1 ppm. I've been keeping up on FC throwing in at least a half a cup of the bleach every time right after soaking in the tub. Today I kept adding a bunch of chlorine through my dose pump and tested afterwards and my tests keep showing no change in FC levels. So then I measured and threw in another half cup myself, circulated and then tested. The half cup I threw in made no difference to the FC level. I just threw in more than enough to bring the FC level up to at least 6 ppm but the test keeps showing somewhere around 1.0 - 1.5 ppm FC. There HAS way more FC in the water than what the test is indicating.

Does that DPD powder ever go bad or lose its potency? The stuff I have is kind of old...

Or am I doing the test wrong?
 
It does. Is it discolored? It should be replaced every year, two at most. Also should be stored in a dry, climate controlled space.
 
Mine goes black after a while and clumps up. But you have less humidity in AB so that would likely be less of an issue.
 
FYI - I also keep some OTO around as well to do the "yellow" chlorine test. It isn't as good as DPD but it is way cheaper and you can buy it more easily in stores. DPD powder is hard to get and wicked expensive in Canada. I normally order test kit refills from friends or relatives that live in the US and have them bring it up when they come for a visit, but that doesn't work so well these days.
 
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