Old claggy DPD powder

[Brad_C]

I've often read provided the DPD powder turns the water pink it's usable.

I have *old* DPD powder. Probably nearly 2 years old at this point. It got claggy so I'd mash it back up with a crusher until it was powder. It turned the water thoroughly pink, although quite dark and left a lot of black residue. It still turned the water pink. I also have a new container of flowing white DPD powder. It also turns the water pink, but a much lighter pink with no residue in the container.

I could not figure out why my FC levels were so low. I thought perhaps my SWG cell was on its way out. I figured I'd try something different, so I took 2 tubes and did parallel tests with old and new DPD powder. To ensure repeatability, I did three back to back tests.

The old DPD powder gave me a reading of 6PPM. The new DPD powder gave me 13PPM.

A DPD tablet from the pool store used in the FAS test rather than the powder also gave me 13PPM.

So at some point, the DPD powder must reach a point where it's "past its sell-by date". I'll admit I was reaching to keep using the remainder of the powder because it "turned the water pink".

As an aside, I could not find anything that would remove the black residue from the test tube. I tried liquid Chlorine, Hydrochloric acid, TSP, Sulphuric acid, Nitric acid and good old mechanical scrubbing (not at the same time). Nothing worked. I figured I had nothing to lose so I tried some Chlorinated brake cleaner. That removed the residue instantly, then dissolved the tube. Whoops.

I keep my new container of DPD powder in a dessicator with Calcium Chloride. Let's see how long that lasts.

 

[DrewLG]

at some point, the DPD powder must reach a point where it's "past its sell-by date".

Recognizing A Compromised Reagent

Taylor Tech Bulletin: Reagent Shelf Life

As an aside, I could not find anything that would remove the black residue from the test tube.

Next time it happens, try rubbing alcohol.

 

[mgtfp]

Interesting. Thanks for sharing that.

 

[Mdragger88]

Next time it happens, try rubbing alcohol

Yes! - or windex (which is also generally mostly alcohol) I also rinse it after.
After the 1st time I cleaned my beaker I couldn’t believe I had waited so long to do it. It’s now a regular habit as it gets darker with time/use. I also go ahead & clean my dipper & the cubby of the storage box with it too.
There’s usually an expiration date on the reagent/dpd containers- I try to verify that it’s around 2 years out when I first get them. If not I return it. Some third party sellers/amazon will ship older products so it’s hit or miss. Tftestkits refills have always been very fresh.
I also try to be very careful that unnecessary moisture isn’t introduced to the powder (having a wet hand, leaving the container open etc) & I keep silica packs in the cubby with it as recommended by others here. I buy other reagents in larger sizes but the dpd powder isn’t one I do that with because of it’s tendency to turn.

 

[woodyp]

I've always thought it was good until it started getting an almost purplish hue.

 

[Newdude]

It's easy and cheap enough for most of us to just replace it. If mine spent that long getting here with no promises the next shipping container wouldn't do the same, I'd use it until the results were off.

Occasionally spot test it by raising your pool a known FC and verifying the powder agrees after the pool has 15 mins to mix.

 

[Brad_C]

Occasionally spot test it by raising your pool a known FC and verifying the powder agrees after the pool has 15 mins to mix.

I could do that, but that'd require I had liquid Chlorine on hand. I've only bought liquid chlorine twice in the last 10 years. Once for a "poo in pool" incident, and once for a SLAM.

I've discovered the old trusty DPD No.1 tablets seem to work just as well, but come in a little foil packet that lasts forever.

100 of those is cheaper than a little bottle of DPD powder (and I don't have to store them in a desiccator), so while I work my way through the current bottle I'll spot check with those, and then I'll probably just use them moving forwards.

Every test I've done with a DPD No.1 tablet in place of the powder has come out the same. Admittedly, I only do a 5ml test also (1ppm/drop) because I just don't need the 0.5ppm resolution and my FC is always > 7ppm. Saves me a lot of titrant.

 

[Newdude]

I only do a 5ml test also (1ppm/drop) because I just don't need the 0.5ppm resolution and my FC is always > 7ppm. Saves me a lot of titrant.

I always say I could give a hoot about the # after the decimal. A 2.5 or a 2.2 still sucks as much as a 2, no matter your CYA level. And a 8 is great for any CYA in range. So yeah. I'm with ya there.

100 of those is cheaper than a little bottle of DPD powder (and I don't have to store them in a desiccator), so while I work my way through the current bottle I'll spot check with those, and then I'll probably just use them moving forwards.

You gotta do what you gotta do with the supplies available to you. The key takeaway here is that you caught the powder being off before it swamped the pool. With regular testing you always have a 6th sense for what the levels should be and can spot that kind of difference.

 

[mgtfp]

I've discovered the old trusty DPD No.1 tablets seem to work just as well, but come in a little foil packet that lasts forever.

Even they don't seem to last forever. I had some old tablets from a Bunnings test kit I had bought years ago, but never really used. When I started titration testing, I thought I could give those old tablets a purpose and use them for drop testing, but they didn't work, didn't turn the water pink anymore. (Edit: I should add that those tablets bleach out much sooner than R-0870, so they can't really be used at higher FC levels).

I also realised that the Taylor powder lasts much longer than CCL's. The reason seems to be that the Taylor DPD containers are coated on the inside with a desiccant which keeps the powder dry for much longer. It also helps that you can open/close the Taylor container with one hand, so you can really minimise the time it's open.

Recently, I found some old CCL DPD powder at the back of the cupboard, that was completely clumped up. Loosened it up and tried a test. It generally still seemed to work, but near the end point, I found it harder to decide whether there is still a hint of pink, or whether that was just dirty grey, so I ditched the powder. But the test result seemed to be within +/- 1 drop to what I was expecting. Certainly not a factor 2 off, as in your case, it must have been not quite as old.

 

[Brad_C]

I don't buy pool stuff at Bunnings because everything they sell seems to be "value engineered" to within an inch of its life. My DPD tablets are Palintest. I haven't had the bleach-out problem yet, but I've never really tried them FC > 10.

The CCL container is certainly not ideal, and yeah the powder I was using was really, really bad. It hadn't occurred to me to try and order the Taylor stuff on line. I might do that next time. I've just checked and these 2 bottles of powder were ordered in Dec 19, so I suppose I shouldn't complain. The first one lasted ~3 years.

 

[YippeeSkippy]

IMG_3953.jpeg

• YippeeSkippy
• Sep 6, 2020

I've started keeping my powder in a tiny Tupperware container along with a few silica packs you get when buying things. Seems to help extend the lifespan of the powder. It fits right into the lid space of my TF-Pro SALT test kit.

Maddie

 

[Newdude]

I use a zip lock baggie with the first couple of little packs that came with something I bought.

 

[YippeeSkippy]

IMG_4292(1).JPG

• YippeeSkippy
• Aug 9, 2022

Neener Neener... mine's more tweaked out than yours!

 

[duraleigh]

TFTestkits guarantees the freshness of the powder for a year from ship date. I don't know of anyone guarantees for two years

we know that chemistry can often be s-t-r-e-c-h-e-d to exceed that performance, However,extending the usage of the VERY important DPD powder adds one more bit of uncertainty that I don't think is a good financial choice.

TFTestkits has an annual Spring Sale (coming up soon) on Refill Sets and starting off with fresh chemistry in all the tests is very reassuring

I think protecting your rather large investment in a swimming pool with Guaranteed Fresh chemistry (especially for chlorine) is more important than trying to stretch out the useful life to the point you have doubts about it.

 

[Brad_C]

TFTestkits has an annual Spring Sale (coming up soon) on Refill Sets and starting off with fresh chemistry in all the tests is very reassuring

Brilliant. When TFTestkits ships to Australia, be sure to let me know.

 

[Sarah and Nate]

Brilliant. When TFTestkits ships to Australia, be sure to let me know.

Unfortunately at this time we have no immediate plans. I know the Australian community is pretty large here on TFP and I would love to serve you all, so I'll be sure to make it known if international shipping becomes a reality.

If it is any consolation for everyone else, we have begun including desiccant packs within the R-0870 powder jar to try to combat shelf life issues.

Nate @ TFTestkits

 

[Charlie Bezzina]

Is this a coincidence? I ordered a new clear choice labs test kit last night because my dpd powder had turned into a sticky lump of purple chewing gum and my test tube has dark purple cancer spots too.

My kit is 1.5 years old and has run out of other chemicals anyway so it needed to be replaced.

 

[Saturn94]

However,extending the usage of the VERY important DPD powder adds one more bit of uncertainty that I don't think is a good financial choice.

This.

 

[Brad_C]

Next time it happens, try rubbing alcohol.

Yowza! That worked a treat. I keep 100% Isopropyl Alcohol around. Put a ml or so of that in the tube and the black (really deep purple) residue just dissolved in front of my eyes.

 

[Scoop]

By coincidence, after reading this thread, for the first time I noticed a light brown ring around the 10mL mark in my Taylor (P/N 9198) Vial. I put some 70% (Gro Store/Pharmacy) IPA on a small paper towel & rubbed the inside of the vial with it & the brown ring is gone. for another great tip from the forum