DPD R-0870 granules consistency and readings.

[calstar]

This 0870 is a new batch, from T-100 refill kit no more than a month old, water samples always taken from the same spot 12-18" deep near a return outlet. In the small tub the 0870 comes in there is typically fine granules and larger coarser granules, I break them up as well as I can but a large percentage of coarser ones remain. I've done this procedure several times and the results are nearly identical. Using the finer grain granules(a few larger ones are presen) , for example, FC is 16 with CC of .5 or less, 0. Using the coarser grain and adding until there is no more color change the reading has been FC 12 CC 1-1.5. I use a magnetic spinner for mixing, the FC level is high because I'm slaming. If I'm adding the reagent(large or small granules) until there is no color change why would the size of the granules make a difference? thanks

 

[DrewLG]

Is it possible that you're adding less when the grains are coarse than when they're fine? If there isn't enough powder, you'll get erroneously low readings -- and especially for higher FC values, you might need more than you're putting in.

You can tell whether you're using enough powder by doing the test and then adding more pool water after the sample has turned clear. If the sample turns pink again, there was more than enough powder and the result can be trusted; if the sample does not turn pink, you didn't use enough powder and the result is suspect.

 

[calstar]

^^^^^ Thanks I'll try that. I don't understand why when using the coarser grains I keep adding until the pink doesn't change more, shouldn't that indicate enough 0870?

 

[calstar]

Did a FC test at 2:45, 17 so I added chlorine @ per PM, after sample went clear I added more pool water immediately turned pink, also tested with coarser granules adding till it was clear, also turned pink with pool water

 

[AUSpool]

This 0870 is a new batch, from T-100 refill kit no more than a month old, water samples always taken from the same spot 12-18" deep near a return outlet. In the small tub the 0870 comes in there is typically fine granules and larger coarser granules, I break them up as well as I can but a large percentage of coarser ones remain. I've done this procedure several times and the results are nearly identical. Using the finer grain granules(a few larger ones are presen) , for example, FC is 16 with CC of .5 or less, 0. Using the coarser grain and adding until there is no more color change the reading has been FC 12 CC 1-1.5. I use a magnetic spinner for mixing, the FC level is high because I'm slaming. If I'm adding the reagent(large or small granules) until there is no color change why would the size of the granules make a difference? thanks

You should be taking the sample away from a return. About 3- 4 feet from a skimmer is usually a good spot.

You add one heaped spoon or two level spoons of the R-0870. We don’t keep adding R0870 until there is no more change in the pink. We then add the R0870 till it goes clear. You can keep going till the last drop causes no change and don’t count that drop.

You can only compare two results from the same sample. You pools FC is constantly changing which is why we test and dose.

It’s best minimize exposure of the R0870, it doesn’t like moisture. Open it, take the heaped or two scoops and close it a quick as practical. If you must give it a grind do it in a dry spot as quickly as practical. Leaving it exposed to moisture should be avoided.

1. Using the small spoon shaped end of the dipper, add one heaping dipper, or two level dippers, of R-0870 and swirl to mix. If the sample turns pink for a moment and then turns clear again, or if it turns brown, add another dipper of R-0870. If the sample remains clear the entire time, your FC level is probably zero, however it is best to verify that with an OTO chlorine test, since the FAS-DPD test is prone to the occasional false zero.
2. Swirling constantly and counting the number of drops as you go, add R-0871 one drop at a time. Continue adding drops until the color changes to clear. The pink color may become extremely faint before it goes away. Make sure that the sample goes completely clear.