Chlorine Test Color as a Function of Concentration

Dirk

Gold Supporter
TFP Guide
Nov 12, 2017
6,904
Central California
? Not quite sure what you're after. You mean a picture of the tester's color scale? Or a bunch of pictures of vials, each with sampled pool water of different FC levels, after the DPD powder has been added?

Or maybe describe what you're trying to learn?
 

PoolNewb2020

Well-known member
May 7, 2020
300
Lathrop, CA
Since that's not how the concentration of free chlorine is measured, I highly doubt there is any reference. But from my experience, the higher the FC, the darker pink the sample turns once the powder is added. But I never had FC higher than 10ppm, so I don't know if it gets even darker pink, or goes to red above that level.
 

Newdude

Well-known member
Jun 16, 2019
4,511
NY
I run a hair on the hot side and it is flaming neon pink colored when i add the powder, but the color isnt important, only the amount of drops to make ot clear.

The OTO drop / yellow / block test on the other hand turns brighter yellow, then orange, then brown as FC increases but its as reliable as a test strip and only good to know there is in fact chlorine in the sample, not how much.
 

Dirk

Gold Supporter
TFP Guide
Nov 12, 2017
6,904
Central California
Since that's not how the concentration of free chlorine is measured, I highly doubt there is any reference. But from my experience, the higher the FC, the darker pink the sample turns once the powder is added. But I never had FC higher than 10ppm, so I don't know if it gets even darker pink, or goes to red above that level.
Are you guys confusing the DPD Test with the FAS-DPD? The latter measures FC by number of drops, the former compares colors. Unless I'm the confused one. Still waiting on the OP to describe what they are after... sounds like their test uses powder. Is there a DPD Test that uses powder instead of liquid, or is powder only used in the FAS-DPD test? I'm missing something...
 
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Smiles79

Well-known member
May 22, 2019
58
Missouri
I understand that the measure of PPM of chlorine in a FAS-DPD test is the number of R-0871 drops required to turn the solution clear. But the solution, once the DPD powder has been added, gets a darker pink as the chlorine concentration increased, and I was curious if there was anywhere out there I could find a scale. Essentially "this concentration looks like this..." and so on with multiple samples.

I'm working on an idea for an automatic chlorine test which would ideally measure the color of the water after the powder was added to measure chlorine concentration.
 

Newdude

Well-known member
Jun 16, 2019
4,511
NY
I'm working on an idea for an automatic chlorine test which would ideally measure the color of the water after the powder was added to measure chlorine concentration.
Have at it and keep us posted. Lots of trial and probably even more error but it will be neat if you can create something.
 
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Dirk

Gold Supporter
TFP Guide
Nov 12, 2017
6,904
Central California
Oh, sorry, so it was FAS-DPD, my bad (well, you bad, as DPD and FAS-DPD are two different tests). As others have pointed out, with the FAS-DPD powder, the color of the pink is not something that is measured. It's the number of drops. If you're trying to build something that measures color, I think you need to be looking at a DPD or OTO test. One is pink, the other yellow? I think I do notice that my "FAS-DPD water" (pre drops) takes on different shades depending on my FC level, and it does get lighter as the drops go in, but I'm not sure that is something to rely on for your purpose. Clearly out of my element in this discussion! I've had a conversation or two with Taylor's head customer service guy (about how their stuff works), who seems to really know his stuff. Perhaps a call to him would help you with your quest.

@JoyfulNoise knows a lot about the chemicals in the tests we all use... Matt?
 
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Newdude

Well-known member
Jun 16, 2019
4,511
NY
Plus, Aren’t there already apps that attempt to read the test strips and fail even worse than the strips themselves ? Don’t get me wrong, I’m all for it if you can pull it off but you’re probably not going to build a better mousetrap here.
 
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santacruzpool

Gold Supporter
Feb 24, 2015
740
Santa Cruz, CA
You can get the Taylor #9056 High Range Test block and use the powder, or the DPD test drops, and easily see the different color intenisities and how they match up to the corresponding FC levels...

I think @JoyfulNoise has posted about using the block this way and other ways to use the powder vs the drops and a high range test block...

I use a High Range Test block on my spa water as it is pretty nice to quickly check the FC levels without needing to do the powder test.

edit: Here is a large pic of the test block:
1598380749873.png
 

Dirk

Gold Supporter
TFP Guide
Nov 12, 2017
6,904
Central California
Now I'm curious. Matt, where are you? Is the DPD powder we get in the FAS-DPD kit the same compound as the reagent drops used in the DPD Test? Like the Taylor K1001? Can they be used interchangeable in Smiles79's quest, to compare the color/intensity of the "pink?"
 

Dirk

Gold Supporter
TFP Guide
Nov 12, 2017
6,904
Central California
Dosing from that is a whole ‘nother story.
I think that is the crux of this effort. If the end result is a gizmo that will tell me close enough that I don't have to get off the couch today, that's one thing. But if the invention is one that would allow me to leave my pool for a week or two and guarantee that my FC will hold the entire time and my pool will be algae free, and swimmable, upon my return, that is another. I don't need the former, I'd pay a bundle for the latter! Please get to work on that, and then a pH version right after. Thanks! ;)
 
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Newdude

Well-known member
Jun 16, 2019
4,511
NY
But if the invention is one that would allow me to leave my pool for a week or two and guarantee that my FC will hold the entire time and my pool will be algae free, and swimmable, upon my return, that is another. I don't need the former, I'd pay a bundle for the latter
When my IC60 reached end of life there was NO question it was being replaced, even as suddenly as it quit. The only question was if I bought this one from that place or that one from this place. Upon telling the Mrs she instantly asked if I bought a new one yet. Not quite yet honey, But thanks for the Approval nonetheless.
 

Chasarms

Silver Supporter
May 8, 2020
347
Dardenne Prairie, MO
I think that is the crux of this effort. If the end result is a gizmo that will tell me close enough that I don't have to get off the couch today, that's one thing. But if the invention is one that would allow me to leave my pool for a week or two and guarantee that my FC will hold the entire time and my pool will be algae free, and swimmable, upon my return, that is another. I don't need the former, I'd pay a bundle for the latter! Please get to work on that, and then a pH version right after. Thanks! ;)
Doesn't your SWCG nearly guarantee that? Of course it could fail, but so could this imaginary gizmo in this discussion.

While I think that is a very cool endeavor, I just don't see a great deal of value. I haven't changed the dosing on my Stenner in weeks. It drops the exact same amount of liquid everyday, and every time I test, I am fine. Never even close to the minimum and only a couple of times have I been less than 1 ppm over the top of the targets. With that in mind, I am completely comfortable leaving my pool for a week and expecting it to be fine when I get back. If I dropped pH to 7.2 before I left, I'd be willing to bet it would be fine as well when I returned.