I can't be the only one with this issue

[duraleigh]

10th drop of R-0871 turn solution clear so I STOP and Record FC as 5.0

Nope. The correct way to perform that and ALL drops based tests is to continue to add until there is NO color change. You say the 10th drop turns the solution clear......that's not the end of the test. You add another drop (and maybe more) until the last drop makes no color change whatsoever. Then you subtract that drop from your total and the result is your FC.

 

[mikemass]

Thanks for the response and clarification. I understand that in any drip titration test this is the most accurate way, because by adding that extra drop and then subtracting it from your calculation you know with 100% certainty where the endpoint is. That is fine if all I wanted to test for was FC and end the test there. But I don't understand how this extra drop doesn't affect the CC portion of the test....

What I was inquiring about is what you do afterward when testing for Combined Chloramines. You can subtract that 1 extra drop from your calculation, but you can't pull that extra drop out of the vial. So when you start titrating for your CC readings, you are already one drop into the titration before you even start. (we added it already going one extra drop past the endpoint in the FC test). Don't we need to account for that drop in the aforementioned CC test? In essence if we test for FC in the same manor we test for CH and TA (one drop past the endpoint) wouldn't your actual CC reading always be 0.5 PPM higher than the calculation?

examples:
If after adding my 5 drops of R-0003, solution turns back to pink indicating the presence of CC's...

I tritrate 2 drops of R-0871 to get it back to clear. But I really used 3 drops because one was in the vial already. So reading for CC is 1.5, not 1.0

If it takes 4 drops to get back to clear, it's really 5 drops, so CC is 2.5, not 2.0

Perhaps this is the reason we say that a CC reading of .5 is acceptable, but over .5 is not? Because there is one drop discrepancy?

 

[Puppiesonacid]

Perhaps this is the reason we say that a CC reading of .5 is acceptable, but over .5 is not? Because there is one drop discrepancy?

Interesting point... I mean... To me having it go clear and knowing it is the last drop is, before it, there is always just a touch of pink at the top of the cylinder, and the next drop it is all gone..

so far trying it with the extra drop, I haven't seen any change after the drop when I thought it was already done.

 

[duraleigh]

What I was inquiring about is what you do afterward when testing for Combined Chloramines.

When you do the test for CC's, simply ignore the FC test. The CC's test begins when your solution turns pink and then you count how many drops it takes to get it back to clear.

 

[mikemass]

When you do the test for CC's, simply ignore the FC test. The CC's test begins when your solution turns pink and then you count how many drops it takes to get it back to clear.

Thanks duraleigh. Even though I am having trouble understanding how an abundance of R-0871 in the vial after doing a Free Chlorine test doesn't impact the CC test I will take your word for it. One thing I respectfully request:

It is likely that new visitors to this site seeking advice will wind up going through Pool School links rather than finding this thread. The FAS-DPD test instructions page, bullet numbers 4 & 5 state that the FC test ends when solution turns clear. It makes no mention of the one extra drop till no further change, then subtract it method:

Pool School - FAS-DPD Chlorine Test

4. 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.
5. Multiply the number of drops by 0.5 to get your FC level

I believe many people find this site looking for advice are very confused about pool care and may be uncomfortable with using a test kit for the first time. Having conflicting information only adds to their confusion.

Please have your IT department make this correction to this page. In the meantime I have contacted Taylor Industries to suggest they do the same to their instructions on their web page:

Instructions

3. Add R-0871 FAS-DPD Titrating Reagent (chlorine) dropwise,
swirling and counting after each drop, until color
changes from pink to colorless. Always hold bottle
in vertical position.

4. Multiply drops in Step 3 by drop equivalence
(Step 1). Record as parts per million (ppm) free
chlorine (FC).

 

[Puppiesonacid]

So confused by FC testing

So yesterday morning, I test the FC after running pump for almost an hour after having it shut off over night. i got a 9.5. I add 3/4 gallons bleach to get it up to 12 for the day. This is using my older bottle 871 and dpd powder

It is 90 and sunny all day. and we went swimming in it last night, didn't check again as it is falling almost right on schedule... and this morning I test it with the new stuff as the old ran out, and I got a FC 13 after running the pump for an hour

So one of 3 things... either the sun never got any chlorine out, or the old test stuff went bad in a few weeks... or my pool is still the pool of mystery.

CYA 100

 

[mikemass]

Re: So confused by FC testing

Consistency is the key. Now that you are into the new bottle of R-0871, continuing using that and only that. Make sure all variables of testing remain the same. Where you pull sample from pool, accurate sample size, the rate at which you allow the drops to fall off the tip, etc.

 

[needsajet]

Re: So confused by FC testing

That's good advice from Mike. Mods will probably move this. It's best to keep it all in one thread. Otherwise anyone looking at the topic is wondering about the background.

 

[Puppiesonacid]

Re: So confused by FC testing

Consistency is the key. Now that you are into the new bottle of R-0871, continuing using that and only that. Make sure all variables of testing remain the same. Where you pull sample from pool, accurate sample size, the rate at which you allow the drops to fall off the tip, etc.

Got ya. But yes, it was tested from the same spot... keeping drops consistent is hard sometimes as, sometimes they come out by themselves... other times they don't, so i very lightly squeeze.

as for sample size... i do my best...

 

[mikemass]

Re: So confused by FC testing

I would say compare the tips of the 2 bottles that you have been using to see if they look the same. (the inside of the tip, not the outside). But that is a moot point now as you won't be using the old one any more. Just stick to the one going forward and see if you get better consistency.

 

[Puppiesonacid]

Re: So confused by FC testing

They are the same. I looked before testing to make sure it wasn't one of the wrong tips.

but yeah, we will see. so if the new tests read higher all the time, it may explain some of the smell of chlorine on the skin, as well as my high PH readings from the older, as the FC may have been higher than I thought... we will find out i guess.

 

[mikemass]

it may explain some of the smell of chlorine on the skin

Not necessarily.....
The smell of chlorine on your skin is actually chloramines as explained in your other thread which I actually just posted in:
Chlorine smell??? On skin

It simply means the Free Chlorine is doing its job. The FC is reacting with impurities on your body. This doesn't mean you are dirty. We all have dead skin cells, are continually emitting fluids in the form of sweat, etc. If you small chloramines when just walking around the pool, that's potentially not good. Means some impurity in the water is reacting with FC. Hope that makes sense.

If you want to do a test, stick your arm in the pool after a long day's work. If you are nice and sweaty, that's better. Now smell your arm. You will get that "chlorine" smell. Next, wash your arm up to your elbow. Wash it real good with antibacterial soap. Now stick that arm in the pool and smell it. If your pool is properly sanitized, you will get no chlorine smell on your arm.

 

[Puppiesonacid]

yeah... but i figured the excessiveness may be due to the higher FC content... but maybe that really has nothing to do with it at all.

 

[Puppiesonacid]

Ok, so whatever the issue... the new testing stuff seems to be doing good. So not sure how far i was really off with the old stuff, or if I just screw up every test in a different way...

But the water is right where it should be now after sitting in the sun yesterday... and another 90 degree day today...