Yellow vs Pink Cl tests?

[Gebo]

Two of my test kits use "yellow" as the color when trying to determine chlorine ppm and another uses "pink" as the reference color.  I see they take different

reagents but what exactly am I checking.  Is one better than the other?  Why would I use one over the other?

[cranbiz]

I would use the yellow simply because the Taylor kits use yellow and I trust the Taylor kits over others.

In reality, as long as all give the same numbers then both should be reliable and you can use whichever kit you wish. Have you tested each with the same water sample? Same water, same results, then use whatever color costs less.

[waterbear]

On 3/23/2024 at 2:23 PM, Gebo said:

but what exactly am I checking.  Is one better than the other?  Why would I use one over the other?

@GeboYellow is (orthotolidine). It is only a test for total chlorine but it does not bleach out at high sanitizer levels. It is useful to see if there is chlorine in the tub. It will also test total bromine. It is usually found in cheap test kits and uses a comparator with yellow color blocks. It can be used to determine if chlorine levels are very high since it will turn dark yellow, orange, and then brown as sanitizer levels go up to about 100 ppm. Not a first choice for testing but can be useful as a backup test and it's better than strips.

Red is DPD (diethyl-p-phenyleneldiamine). It uses a comparator with red color blocks. It can test both free chlorine and total chlorine. Combined chlorine can be determined by subtracting the free chlorine reading from the total chlorine reading. It will beach out at high sanitizer levels (bleachout can start at sanitizer levels of 5 to 10 ppm depending on the maker of the test) leading you to believe that your sanitizer is low or nonexistent when, in reality, it is high (which can also give you false high readings on pH tests). It can also test total bromine. It cannot test high sanitizer levels because of bleachout without diluting your sample with distilled water, which is a cumbersome process. It can give false high readings when MPS and ozone are used since they both test as chorine/bromine. Taylor does have a reagent pack that can remove the interference from MPS. Many men are unable to differentiate between close shades of red and find the DPD test difficult to read. Women are much better at differentiating close shades of red. DPD is the most common testing method used by most testing supply sellers (Taylor, LaMotte, Hach) and is also used in some strips.

FAS-DPD (Ferrous ammonium sulfate/diethyl-p-phenyleneldiamine) is the gold standard for sanitizer testing. It is not a color matching test. It is a titration (drop counting test) that has a distinct color change from red to colorless that even color blind individuals can see and a precision as good as .2 ppm (for chlorine) or .5 ppm (for bromine). It can directly determine free chlorine and combined chlorine with no math and can also determine total bromine. It does not have the same bleachout problem (if it flashes pink and then turns cloear add more DPD power until there is a stable pink color) and can test much higher sanitizer levels (at least to about 20 ppm or even higher). AFAIK, only Taylor Technologies offer FAS-DPD test kits. FAS-DPD is used in their K2006 and K-2106 kits (which are the ones I recommend) and as  stand alone kits.

I would recommend FAS-DPD weekly and use OTO as a quick check to make sure sanitizer is present for daily testing or if you think sanitizer levels might be very high. before checking pH since you cant test pH when sanitizer is above 10 ppm (for Taylor pH reagents, some other brands of pH test become unreliable when sanitizer is above 5 ppm and some of the cheap ones 3 ppm, making them fairly worthless.

 

4 hours ago, cranbiz said:

Taylor kits use yellow

@cranbiz Nope! Most Taylor kits use either DPD or FAS-DPD,  only a handful of their kits use OTO. OTO is pretty much considered obsolete these days since it can only test total chlorine.

[Gebo]

Isn’t this one of the “good” Cl test?

 https://tftestkits.net/FAS-DPD-Chlorine-Test-Kit-p47.html

 

This is the one that turns from pink to clear in one drop.  

[waterbear]

They buy Taylor reagents and equipment in bulk and repackage the so it's essentially a Taylor kit. If you look at the R-0003 reagent it is the Taylor reagent bottle! Like I said Taylor is the only company offering FSD-DPD testing. I don't count a repackaged Taylor kit as a separate manufacturer.

To answer your question, yes this is the FAS-DPD titiration test with a color change from pink to colorless It is not" in one drop" as you stated. You count the drops and each one represents either .2 ppm when you use a 25 ml sample or .5 ppm when you use a 10 ml sample. IMHO, .5 ppm is more then enough precision for a pool or chlorine spa. If you are testing bromine then the 25 ml sample is better because if you are using this test yo would multiply .FC reading by 2.25 to get total bromine and if you are using the bromine specific test (only available from Taylor) then it will give you a precision of .5 ppm.

.

[Gebo]

What I was trying to say is one drop causes the color change.  1 drop equates to .5 ppm.  This morning I used 5 drops for a 2.5 ppm Cl