FAS/DPD and TA test questions

[rimshaker]

Got my TFkit today. Last I remember being this excited was in my chemistry labs. Every test is straightforward but I got questions:

1) FAS/DPD. When I start counting R-0871 drops, is the endpoint when the mixture is as clear as the original water sample? Or will there still be a very slight residual pink hue? I was throroughly swirling after each drop. I added 2-3 extra drops but the light pink hue never went away.

2) With the DPD powder, what exactly is a "heaping scoop?" Is it a level scoop? Or a scoop with a little extra mound on top?

3) TA. When counting R-0009 drops, is the endpoint when a drop finally produces an instant red cloud? Because the red cloud disappears after a little swirling around. Or is the endpoint when the entire mixture is red, even after swirling several times?

 

[duraleigh]

Rimshaker,

The FAS/DPD test should turn completely clear. If you let it sit, it seems I remember it will turn back slightly pink. You should drop and swirl and it should clear completely for at least 10-15 seconds or so. Waterbear is the guru on this so let's get his opinion as to why your pink is returning.

TA is a little easier....you want the complete color change and you want it to stay.

Yeah, I still like the "mad scientist" aspect of the kit after five years.....enjoy! :lol: :lol:

 

[JasonLion]

On the DPD powser, the Taylor directions say two level scoops. Leveling the scoops is annoying and one overflowing scoop is about the same as two level and easier to do so TF Test Kits changed the directions. Apparently all you really need is enough to turn the sample an obvious pink, which is sometimes one scoop and sometimes two and sometimes more (unless FC is zero in which case it will never turn pink).

 

[KurtV]

...
3) TA. When counting R-0009 drops, is the endpoint when a drop finally produces an instant red cloud? Because the red cloud disappears after a little swirling around. Or is the endpoint when the entire mixture is red, even after swirling several times?

It's when it turns completely red and stays that way. Also, per Taylor's website, you should add drops and swirl until the last drop produces no more color change. In their words, "When you think you’ve reached the endpoint, add one more drop of titrant to be certain the color change is permanent. If the color remains unchanged, do not count this last drop."

Edit: Sorry, I see now that Dave already answered that one.

 

[Guest]

The endpoint on the FAS-DPD test is when the color changes from pink ot clear. The pink color will reappear on standing so it is important to do this test and not let the sample sit inbetween drops. Once it turns clear add 5 drops of the CC reagent and if it turns pink again then retitrate to get the CC reading.

 

[Shelley N]

I have always used one level scoop. My solution has always turned pink. It is, however, a lighter pink when the CL is reeeeeeeally low.

 

[rpgman]

I have always used one level scoop. My solution has always turned pink. It is, however, a lighter pink when the CL is reeeeeeeally low.

I use the Taylor FAS/DPD kit, and I always use 2 level scoops of the power.

 

[Rangeball]

One scoop, two scoops... Does it make a difference in the final result if it turns a good pink color then clears after adding X drops?

 

[JasonLion]

The amount of powder doesn't really matter as long as your sample turns pink. When the chlorine levels are really high you will need more powder than you need with normal chlorine levels.

 

[rpgman]

The amount of powder doesn't really matter as long as your sample turns pink. When the chlorine levels are really high you will need more powder than you need with normal chlorine levels.

I guess that's why I always use 2 scoops cause I'm always running at around 8ppm with a CYA of 35

 

[waterbug]

Yes, but by adding more stuff to make it still pinker don't you need more reagent to turn the water clear again, and thus, affecting your numbers? Or does it only get so pink, so one scoop will do and the test results will equal the same whether you use one scoop or two?

 

[JasonLion]

Think of it this way: When there is one chlorine next to one bit of powder it turns pink. When there are no chlorines it is clear. When there are two or more chlorines it is clear. So you need more of the powder than there is of chlorine. Then the tritrant drops destroy a little bit of chlorine with each drop till there isn't any more and it is clear again.

 

[waterbug]

Sorry i'm not understanding that. If I put in more of the stuff that makes it turn pink, does it not then take more of the drops to make it clear again and so your readings are off?

If i put in less, then I have less drops to add and then my chlorine numbers are very low, put in more and the numbers are high/ i am definitely confused here.......this is because I tested chlorine to be around 11 and the pool store got 3.?

 

[Rangeball]

waterbug, I think he means you can only turn it so pink. Only so much chlorine is present, so once it hits a certain threshold, more powder is only wasted, as there is no chlorine left for it to react and turn pick with so it is ignored in the drop counting, which is neutralising the dpd powder bound chlorine.

 

[waterbug]

okay, i guess I see that, but how does one know how pink is pink enough then? Just add one dipper full and if it pink start testing?

 

[duraleigh]

Just add one dipper full and if it pink start testing?

Yep! :lol:

 

[Rangeball]

I got DPD powder before I had a scoop. I just slowly added some, until it turned just pink, and tested. Got a dipper scoop, and added one level scoop, to my pool sample with 3 ppm FC and my dads with 18 ppm, and got the same much deeper pink. End result in my pool was the same as it should have been.