CH Vanishing Endpoint- Do Anything?

[LMK17]

I was having a heck of a time with the CH test and vanishing endpoint issue. I finally settled on a procedure that works: Pool water diluted 1:1 with distilled water, 10 ml sample size, and pre-treat with 3 drops of R-0012. I get a nice, permanent color change to blue, and I’m confident in my CH result.

My question is, should I try to treat the metal ions that are apparently present and interfering with the CH test? I suspect iron is the culprit, as I know our well is high in iron. We recently replastered the pool, and although I filled the pool about 2/3 with filtered well water, the final 1/3 or so is unfiltered. The pool folks added 1 gallon of Startup-Tec to the newly filled pool. Should I add another dose of sequestrant or try to otherwise treat the (presumed) high metal content in the water? I do top off the pool with filtered, softened water, so hopefully no additional metals will be added on an ongoing basis.

 

[Texas Splash]

Perhaps @JoyfulNoise can confirm your process and questions.

 

[JoyfulNoise]

The testing procedure is fine. Taylor typically recommends 3 to 5 drops of R-0012 initially. So you’re testing method is solid.

I would suggest getting the pool water tested for metals to see where the level is at. It may not need to be treated and so, if you can avoid getting hooked on sequestering agent, the better off you’ll be.

 

[stevo777]

doing the same thing, pretreating with 5 drops of R-0012. Not doing a 1:1 dilution, hadn't heard of that trick. Despite that, when adding, color goes purple, and then after 2-3 more drops, goes to a definite blue. when totaling up all the drops, i'm at 300-325 ppm. Is the transitional purple acceptable?

I know we have high iron content in the water, just look at all the red rock around here....

 

[JoyfulNoise]

The endpoint of the CH test is BLUE. Period.

The indicator dye is red when calcium and magnesium are present and blue when they are not. The moment you add the dye the water sample should turn red since calcium is present (magnesium is removed by the R-0010 buffer). As you start to add the titrating reagent, the solution will be a mixture of red and blue and so it will look purple. The red color of the dye tends to be more intense than the blue so the purple color will persist right up until the titrating reagent has chelated the last of the calcium ions. The blue color tends to be a lighter, baby blue.

 

[JamesW]

Should I add another dose of sequestrant or try to otherwise treat the (presumed) high metal content in the water?

Do you have a cartridge filter?

If yes, can you show a picture of the cartridge before cleaning?

 

[LMK17]

I would suggest getting the pool water tested for metals to see where the level is at. It may not need to be treated and so, if you can avoid getting hooked on sequestering agent, the better off you’ll be.

What is the preferred method for testing for metals? Is there a recommended test kit?

Do you have a cartridge filter?

If yes, can you show a picture of the cartridge before cleaning?

Yes, and sure:



This filter was about 1 week out from its previous cleaning.


As always, thanks for the replies!

 

[JamesW]

Copper is usually the cause of fading endpoint, but that looks like mostly iron.