Saving R-0871

[nlindelldc]

Well I searched several threads but I just want to make sure I got this correct:

In order to save a little R-0871 reagent, I can use 5 ml of pool water and 5 ml of distilled water (to total 10 ml). If I do this, then however many drops I add is my actual PPM chlorine, is that correct?

For example, I added 14 drops before it went clear so my FC is 14? (as opposed to 7 if I had used 10 ml of pool water)

(I know it's not quite as accurate, just trying to save a little until my order of more comes in)

 

[pabeader]

That is correct. But you really don't need to do the dilution, you can just do the 5ml and each drop is 1 ppm
You just need to take great care with the meniscus. Or have a very good way to accurately measure a 5ml sample of pool water.

 

[nlindelldc]

That is correct. But you really don't need to do the dilution, you can just do the 5ml and each drop is 1 ppm
You just need to take great care with the meniscus. Or have a very good way to accurately measure a 5ml sample of pool water.

Thanks Pa, great advice as usual! I think I might use a small syringe to get exact 5ml

 

[singingpond]

Syringe is a good idea - I use one (left over from some children's liquid meds) for all test samples - 5 ml, 10 ml, 25 ml, whatever. Much more controllable and accurate than trying to get the meniscus exactly in the right place.

And, as stated, no need to dilute your 5 ml sample with distilled water - that would be an unnecessary extra step.

 

[kywildcats]

I only thought the meniscus was relevant in the daily chlorine and PH, two cylinder tester?

 

[jblizzle]

The bottom of the meniscus is always the important level.

 

[singingpond]

I only thought the meniscus was relevant in the daily chlorine and PH, two cylinder tester?

The quantity of water you use matters in all the tests; the more repeatable your water measurements are from test to test, the more reliable your results. "Meniscus" is just a word for the top surface of the column of water in its container, so that's always what you're looking at when you check if you have the proper quantity of water in your testing container.

Come to think of it, I use the syringe for direct measurement of 5 ml and 10 ml samples; for larger samples (CH and TA tests) I watch the meniscus while using the syringe to slowly add the last bit of water to reach the desired level - much slower and more controllable than just pouring the water into the testing container.

 

[pabeader]

Purests would say this; "Sample must be measured with the meniscus at eye level (to eliminate parallax error) and at the center of the meniscus, i.e. the top of a convex meniscus or the bottom of a concave meniscus."