DPD powder experiment

[Poconos]

Interesting about the 1/3 decrease in reading. I still have the powder samples and will try a couple more comparisons, probably at end of this season and next year. Chemistry isn't my bag so I have no idea. Chem_Geek...any thoughts on this?
Al

[PatL34]

I have started to keep the DPD powder vial in a silica gel bottle, and am waiting to see how it turns out.

Pat

[waterbear]

My understanding is that as long as the color has not turned to a dark grey it is still usable. Light grey and clumpy is ok.

[Poconos]

I think the 'bad' powder is obvious. Form your own opinion. Best I could do for lighting and a gray scale without fussing too much but it is white to black. I know...I've got to get a life. But...this is fun stuff.
Al

Attachment 450

[CrisL]

Earlier I indicated that I kept a container of the dpd powder for over one year before degradation. The stuff I have now I bought two years ago and lasted two full seasons, with what appear to be accurate results (add 5 ppm of bleach, get a 5 ppm rise in measurement). I keep it in a dry location on the bottom floor of the house. I do not put my test vials in the kit container so there is no moisture locked in. I am looking forward to Al's report on the stuff he keeps in the fridge.

[Poconos]

A final followup on the original experiment. The caked, dark DPD powder that was used in the original test was now a hard chunky lump that had to be ground up. Yesterday did a 25 ml sample test of that vs. good powder and the results were the same at FC=1.0 Today, after bringing up the FC, both measurements were 3.6 So.....looks like the DPD powder is pretty stable even though it looks pretty bad. I certainly don't recommend letting the powder get this bad but some dark gray discoleration should be nothing to worry about.
Al

[waste]

Thanks for the experiment and the results !!!