how much 0870 powder

[boondog]

i have been using one scoop to turn it pink but i saw somewhere to use two. As long as it's pink does it matter?
thanks

 

[chem geek]

If you are using a 25 ml sample size then you should use two scoops. If you are using a 10 ml sample size, then two scoops will give a darker more clear endpoint, but usually one scoop is sufficient and will give you nearly the same result. You can experiment using a 10 ml sample size both ways (one vs. two scoop) to see the difference in readings. The purpose of the powder is as an indicator dye and since you are just looking for a transition from colored (pink/red) to clear, the amount of dye isn't critical. You just need enough for the "last drop" transition to be reasonably distinct.

As an extreme example, if you were to use a fraction of a scoop of powder, then the sample would be so faint, especially as you were getting towards the end of the test, that you would have a hard time seeing it go from pink to clear and you'd probably underestimate the chlorine level. At the other extreme with excess powder, the transition would be easy to see but you'd use more powder and it's possible that there might be some residual faint pink remaining as visible (this last effect is speculation on my part and may not occur).

Richard

 

[Bama Rambler]

The reference to using one heaping or two scoops comes from IIRC the instructions for the different kits. The Taylor K-2006 calls for two scoops and the TF100 kit calls for one heaping scoop. It amounts to the same thing really.

Chem Geeks posts goes into the why's and wherefores and should help you understand the process. I know it sure does me. :-D

 

[fordsbyjay]

You only need 1 scoop using the small end if you have the TF100 kit. There was a post I read where someone was using the large end and ran out.

 

[PaulR]

Yes, you grab the flat part and scoop with the dimpled part. I usually scoop once but don't bother leveling it; if my levels are really high then I'll mound it up more.
--paulr

 

[Beez]

One scoop...two scoops...these are only guidelines. The repeatability of the FAS-DPD test is +/- 1 drop and there is only one way to know if your method can reproduce this accuracy. Test it! How many of you took the time and effort to do repeat tests to see if your method is accurate?

The amount of powder is only one variable that can affect the accuracy of this test.

 

[chem geek]

I forgot to mention that when chlorine levels are very high, then if one gets a flash of pink that goes away (before adding any titrating reagent), then add more powder until the color holds.

 

[stev32k]

I've seen a reference to using a 25 ml sample several times. Why is that done - more accurate? And how many scoops are needed if using 25 ml?

 

[frustratedpoolmom]

It's to test up to .2 for accuracy instead of .5 Use two scoops for this sample.

 

[PaulR]

More specifically, with a 25ml sample, each drop of R-0871 counts as 0.2 instead of 0.5. So you use a lot more drops. There is rarely any reason to test with 0.2 granularity.
--paulr

 

[fordsbyjay]

How many of you took the time and effort to do repeat tests to see if your method is accurate?

I sure did.

 

[PaulR]

Well, yeah, what good is a new toy unless you play with it? :-D
--paulr

 

[boondog]

I ordered 2 Oz. of 0871, when that gets here I will do testing for repeatability. In fact I have several methods and chemicals to test against each other.

 

[Cherie]

boondog, that's what I did last summer too. I went through a lot of the test stuff and by the end of summer, I felt very comforable with my ability to perform all the tests correctly.

 

[TomU]

I did some testing awhile back. I did 13 tests in a row using brand new chemicals. 11 of the tests were done with a 25ml sample and 2 of the tests were done with a 50ml sample. (For the 50ml tests, I doubled the powder, and counted each drop as 0.1ppm.) I did find that using two heaping scoops instead of two level scoops would make the test results show about 12% more chlorine available (7.2ppm - 36 drops vs 6.4ppm - 32 drops). I was extremely careful to rinse out the tube with pool water several times between each test. I was also very careful to get the water level exactly on the proper mark. I am fairly confident that the variation I saw between the heaping tests and the level tests were caused solely by the difference in powder quantities. I'm about ready to order some more chemicals. Maybe I'll order some extra and do this more extensively again.