Testing Chlorine

[congachile]

I have a question about chlorine testing. I bought a Taylor kit last year on TFP's recommendation and it has been a great help keeping my water balanced, although I have a heck of a time keeping iron staining out. I think I found the source after many months; it seems to be the oak leaves from the trees in my yard. Lots of trees and it's a full-time job keeping them out. But not really what this question is about. I test a lot in order to keep the chlorine and pH at a minimum to keep the staining at a minimum. While testing today, I wondered why all the other tests seem so precise, but chlorine is two "dippers" of DPD powder. I've watched videos of people doing the test and some use almost overflowing scoops, some less so. What gives?

 

[PoolStored]

If you read the taylor instructions for the 25ml sample, they clearly specify that you "add two dippers of powder to the test solution". That is two (2) dippers, FULL STOP. You do not modify the amount of powder regardless of the sample size. The R-0870 powder is actually a mixture of several different chemicals, not just the DPD dye. The chemical makeup is designed to adjust the pH of the test sample to right range and buffer the pH during the test. There are also chemicals in there to protect against interferences from metals. So using less than the prescribed amount of R-0870 can possibly lead to trouble. There's a lot of anecdotal stories on TFP about being able to use less powder to "save" on reagents; I would assert that you should simply follow the instructions as-written.

One dipper is plenty for 10ml sample.

Heaping dippers will not harm the test, they will just stay ndisolved…

 

[Newdude]

I test a lot in order to keep the chlorine and pH at a minimum to keep the staining at a minimum

You want more chlorine to lift tannin stains, not less. If FC level and Ph seem related to the stain occurances, that points to metals.

 

[dereksanders]

The 10ml sample size also saves on reagents.

 

[AUSpool]

I have only ever used one scoop in a 10ml sample. If it turns pink and stays pink you’re good. A 0.5ppm resolution is more than enough for normal testing. For me it’s about getting that scoop out and close up the container. Dry hands and don’t fuss over it, I’m probably using one heaped scoop.

Water Testing Instructions - Further Reading

www.troublefreepool.com

I test a lot in order to keep the chlorine and pH at a minimum to keep the staining at a minimum.

You don’t want to stay at your minimum, thats asking for trouble, particularly if you have excess organics. Treat your minimum as your bottom line you never cross. If I’m ever at my minimum it’s time for immediate attention, add some chlorine, turn my SWG up a little and test again tomorrow. Try to stay at or above your target level for your CyA.

 

[congachile]

You want more chlorine to lift tannin stains, not less. If FC level and Ph seem related to the stain occurances, that points to metals.

It's not tannin, it's iron. I was confused too, but after researching, I found that our water supply apparently doesn't have iron, but oak leaves do.

 

[Newdude]

I found that our water supply apparently doesn't have iron, but oak leaves do.

I mean. It makes sense after the fact as we all do, but that's my Google learn of the day. THANKS.

Let's page @JoyfulNoise for his thoughts if the iron content is enough to matter. Usually we raise the FC to remove the tannin stains which would then possibly cause iron stains robbing Peter to pay Paul. Hang tight.

 

[congachile]

If you read the taylor instructions for the 25ml sample, they clearly specify that you "add two dippers of powder to the test solution". That is two (2) dippers, FULL STOP. You do not modify the amount of powder regardless of the sample size. The R-0870 powder is actually a mixture of several different chemicals, not just the DPD dye. The chemical makeup is designed to adjust the pH of the test sample to right range and buffer the pH during the test. There are also chemicals in there to protect against interferences from metals. So using less than the prescribed amount of R-0870 can possibly lead to trouble. There's a lot of anecdotal stories on TFP about being able to use less powder to "save" on reagents; I would assert that you should simply follow the instructions as-written.

One dipper is plenty for 10ml sample.

Heaping dippers will not harm the test, they will just stay ndisolved…

I get that but "dipper" doesn't really seem to be much of a measured amount. I use two dippers, but what does that really mean? Also, the powder seems to collect in my dipper and it's difficult to get them very clean so as to get a full "dipper" amount. My guess is most people don't clean and scrub their dipper after using it. I've done that and it collects around the inside of it again after one use. If the amount heaped into it doesn't really matter, then I guess you've answered my question. Thanks.

 

[Newdude]

I use two dippers

And i use a 'heaping scoop' so in the end we both have a little snowballs worth.

Also, the powder seems to collect in my dipper and it's difficult to get them very clean so as to get a full "dipper" amount

Mine does too and it usually comes right out with a quick dip under a faucet. If not I grab a point knife and it scales out easily. (Then immediately starts growing again)

If the amount heaped into it doesn't really matter, then I guess you've answered my question.

Once it goes Barbie pink, you used enough. Any extra doesn't really dissolve and you can judge your dose by whether it's got a couple grains swirling around, or mud.

 

[JoyfulNoise]

The “dipper” is a 0.5mg scoop (it’s printed on the plastic). Each “scoop” is roughly 0.5mg of powder. The indicator reagent is added “in excess” as most indicators in chemistry are - it’s not the amount of indicator that matters it’s how much of it reacts with what you a trying to measure. Since what you are trying to measure is an unknown quantity, you have to add an excess amount of the indicator in order to make sure you get consistent results.

Yes, almost all living matter on earth uses iron (and other multi-valent metals) for biological processes but that doesn’t mean you will get iron stains from them.

Given that you live east of the Mississippi River, your water, no matter where it comes from, likely has lots of iron in it. Iron is not considered a contaminant by the EPA and water suppliers are not required to treat for it or even report its levels if they don’t want to. So it is more likely than not that your water source is the culprit rather than oak leaves. If the stain reacts to vitamin C y disappearing, then it’s iron and not tannins. If the stains lighten with exposure to high chlorine levels, then its tannins.

 

[AUSpool]

I think the precise part was answered but I was working on this last night before I ran out of steam so I thought I’d post it anyway.

The FAS/DPD test is arguably the most accurate and precise test we have. It has a resolution of 0.2 or 0.5ppm while most of the other tests are 10ppm or greater. I guess it just seems less precise because it’s the only one where the indicator is added as a solid but from above the exact quantity of the indicator doesn’t affect the outcome as long as there is enough. In this case the indicator is the DPD, a chromogenic indicator (N, N-diethyl-p-phenylenediamine), if the sample turns pink and stays pink there is enough. As with all the titration tests the result is calculated from the final volume of titrant used. For the FAS/DPD test the titrant is the FAS (ferrous ammonium sulfate) and the end point (pink to clear) is quite well defined.

 

[congachile]

The “dipper” is a 0.5mg scoop (it’s printed on the plastic). Each “scoop” is roughly 0.5mg of powder. The indicator reagent is added “in excess” as most indicators in chemistry are - it’s not the amount of indicator that matters it’s how much of it reacts with what you a trying to measure. Since what you are trying to measure is an unknown quantity, you have to add an excess amount of the indicator in order to make sure you get consistent results.

Yes, almost all living matter on earth uses iron (and other multi-valent metals) for biological processes but that doesn’t mean you will get iron stains from them.

Given that you live east of the Mississippi River, your water, no matter where it comes from, likely has lots of iron in it. Iron is not considered a contaminant by the EPA and water suppliers are not required to treat for it or even report its levels if they don’t want to. So it is more likely than not that your water source is the culprit rather than oak leaves. If the stain reacts to vitamin C y disappearing, then it’s iron and not tannins. If the stains lighten with exposure to high chlorine levels, then its tannins.

Well, thanks for the responses, everyone. If I had known that I would be constantly battling iron stains, I would have gone for the granite, instead of the sully blue. It looks great when it's not stained, but kinda dull when it is. I guess it gives me something to do.