DPD Powder Question

[DavidD]

Last season, after dumping DPD powder all over the place, I found myself in the same situation. After going to the local pool store and buying DPD powder from them, I noticed the scoop it came with was smaller. I continued using my PS233 scoop all last year. This year, after ordering more from Ben, I decided to compare and noticed no difference in readings (up to 11 ppm FC) using the Taylor Scoop and the PS233 scoop. I started off this year using the new smaller one thinking that I might stretch the powder out a little further then switched back. I personally prefer Ben's scoops as they are a little longer however with the lesson learned, I don't fill the scoop all the way up. One thing I did like about the Taylor was that it had a "coating" on the inside to absorb moisture. I noticed that Ben has started putting little silica pouhes in his now as well.

Dave

[bassadict69]

Mine got dumped also!

So, you are saying using the other powder that it did not matter which scoop you used? Was the other powder you ordered finer than the stuff in the test kit?

[CarlD]

Curiously, the amount you use of the FAS-DPD powder isn't critical. You need enough to make the water turn pink. That's all. More doesn't make it pinker or affect the reading--it just wastes powder.

[bassadict69]

That is good to know Carl. I thought I had read on here to be sure to use 1 level scoop.

Thanks guys for the help!

[AndieP]

Curiously, the amount you use of the FAS-DPD powder isn't critical. You need enough to make the water turn pink. That's all. More doesn't make it pinker or affect the reading--it just wastes powder.

That good to know....so I really can use just 1 scoop of powder with the Taylor 2006 kit instead of 2? I tried it tonight and the water turned pink with just 1 scoop. Thanks!

[Watermom]

Yes. As long as the water turns pink with one scoop, that is all you need. It will make your powder last longer.

[Mom2Czars]

The kit from the store said to use 2. I was just thinking this morning that I was going to run out at the rate I'm testing. (who's obsessed? not me.)

[CarlD]

Trust us...All you need is enough to turn the water pink. More doesn't have any effect--other than to use up the re-agent. I use one scoop all the time.

[DavidD]

The kit from the store said to use 2. I was just thinking this morning that I was going to run out at the rate I'm testing. (who's obsessed? not me.)

I know what you mean about the obsessed part. I test way more than I need but it just doesn't take that long to do and I'm taking Carl's "stay ahead..." advice to heart. Any time I test for CL using OTO, I also test using FAS-DPD since there isn't any "shade" matching involved. It's either pink or clear, cut and dry.

Dave

[PoolDoc]

General notes about DPD powder:

1. Those who said that if the sample turns pink, no more DPD is needed are probably right. But, I'm not entirely sure of that. More below.
2. The quantity of powder in TWO Taylor scoops is approximately the same as in ONE of my scoops. When I switched to my own container serveral years ago (after Taylor adopted a container that guaranteed spoilage of the powder) that was the smallest scoop I could find.
3. Moisture is what kills the powder. After years of being told it wouldn't help, I finally put the desiccant packs into my containers. The very next season, Taylor added desiccant lining to their container, when they replaced the horrible container that had prompted my switch to my own containers.

By the way, thanks for the info about dumping DPD powder. It had never even dawned on me that that could be an issue. I'm sometimes all thumbs, but it happens I've never done that, and it just didn't occur to me. I'll have to think about that, and see if there's a way to avoid that problem.

Ben
"PoolDoc"


More about the powder:

All of the Taylor tests I use -- OTO, phenol red, ALK, CAL, CYA, SALT -- EXCEPT the FAS-DPD are essentially industry standard tests. They've made a few modifications, like stabilizing the phenol red a bit against high chlorine levels, but mostly, they are standard reagents used in standard ways. However, the FAS-DPD test does not appear to be standard. Using ferrous ammonium sulfate with DPD is standard method, but as a rather complex lab method which requires use of upwards of 7 different chemicals. Taylor's done some proprietary blending and buffering to reduce this to just two reagents -- the DPD powder and the FAS solution. But, unlike the other chemicals I use from Taylor, I do NOT know exactly what's in either one.

I've looked, but as far as I can tell, this test is unique to Taylor. Hach sells a DPD powder for use in it's colorimetric (color matching) tests. LaMotte and Palintest sell the DPD tablets originated by AT Palin, the originator of the DPD method. But only Taylor seems to have the simplified titrimetric test used in my PS23x series kits.

The DPD powder is mostly NOT DPD! It actually contains much less than 1% of N,N-Diethyl-p-phenylenediamine which is the actual DPD indicator. The rest is phosphate buffers, metal sequestrants, and other unspecified 'stuff'. They do NOT share the details of what this 'stuff' is, nor how it affects the test.

For this reason, I'm not entirely confident that it's always safe to say that, "If you get a pink color, all is well". I'm pretty sure that that's true if chlorine levels are 5ppm or less, but I'm much less sure when chlorine levels exceed 15 ppm!