R-0870 degradation and end of useful life

[Fuldo]

I've noticed that Taylor R-0870 powder starts out white but slowly turns gray as it ages. I suspect that exposure to moisture causes this because I've noticed that it happens more quickly when used frequently and when used in more humid regions. However, even when somewhat gray after a year or so it seems to work properly although I have noticed a slight delay in the color change to pink after adding it to the water sample.

Does anyone know what chemical changes may be happening that causes the powder to gray-up? Also, how does one know when it has "expired" and may not be working properly or giving accurate results? I've gotten to know my pool rather well and don't need to test for chlorine that frequently so a container of R-870 might take 2 years to use and I'd hate just waste it just because it doesn't look right but seems to work properly.

 

[tim5055]

Even when grey and crumbly it has always worked fine for me. I know my last one lasted close to 3 years.

 

[AUSpool]

From the safety data sheet the fresh state is a white powder. Heat and moisture cause it to turn grey. If left too long it will eventually turn a dark green/purple or black which is probably time for a new batch. I beleive the Taylor R0870 powder bottle has a desiccant feature built into the bottle. The DPD powder has about 5-6 ingredients so there is likely to be several reactions going on but avoiding moisture and heat is the take home message.

 

[Killer95Stang]

Moisture is probably the biggest factor in how fast it goes bad. I recently ordered a refill set and when I pulled it out of the bag, the powder was dry, purple and clumped like cat litter. I noticed that the lid was very loose, so that was probably the source of the moisture that was wicked into the container. Of course, one email later and I had a new replacement bottle on its way. Thanks again TFKits for handling the minor situation.

 

[duraleigh]

If the R-870 powder turns your solution pink (assuming you have SOME chlorine), the powder is viable and the test result valid......regardless of the color of the powder. Moisture (humidity) is the culprit for the powder darkening over time.

 

[Fuldo]

Thanks to all for the information. It will be interesting to see how this container ages and if/when it becomes unusable. I now know I can trust it if it reacts with the water. I was mostly worried that the accuracy might be off when old and if so that would put me at risk because sometimes I let the FC level drift to near the absolute minimum.

 

[AUSpool]

If the R-870 powder turns your solution pink (assuming you have SOME chlorine), the powder is viable and the test result valid......regardless of the color of the powder. Moisture (humidity) is the culprit for the powder darkening over time.

Good to know, I scrolled through heaps of old threads and didn’t find this. Given that the DPD sulfate salt makes up ~1% of the total, if the powder is black and absorbed or adsorbed moisture, increasing weight and volume, would it be wise to use two scoops if the powder is black?

 

[duraleigh]

would it be wise to use two scoops if the powder is black?

Typically not. Somewhat surprisingly, the amount of powder is not critical to the test......that's why we use a "scoop" and not an exact amount.

All you are looking for is the solution turning pink. You will most likely have some undissolved residual powder in your test vial......that's OK, too.

On a side note, the most common error we see on that test is a complaint that the powder is bad because no amount of scoops results in ANY pink.........most always that's because there is ZERO chlorine in the pool! Use the OTO chlorine test to detect the PRESENCE of chlorine if you get no pink color from the FAS/DPD.