Water Testing Questions

[DickP3]

My TF100 kit arrived yesterday and I am pleased with its reproducibility for FC, CC and TA (those are the only ones I did in duplicate). Both sets of answers were exactly the same.

My results were: pH 7.2; FC 5.5 ppm; CC 1.0 ppm; TA 60 ppm and CYA >100.

Do you recommend drying the measuring vials with a paper towel when storing

or just air dry. I thought capping them when damp could cause problems.

For a hot tub, what temperature should the water be for testing? Do you

need to wait for it to get to room temperature?

Any other suggestions will be appreciated.

Thanks

[Emprov]

When I used to maintain pools, I never dried the kits out and never had a problem. I'm guessing that, because the water that is being tested has chemicals in it to kill the kind of stuff that would otherwise be problematic, you'd be fine by just putting it away wet and rinsing in the spa water before testing. And test the water at spa temperature. It seems to me that the longer the water is out of the tub, the less it resembles the water that's actually in the tub.

[chem geek]

You can just air dry them after rinsing them out with tap water (or filtered water, if you've got that at the sink). I'd leave them uncapped, however.

You should generally let the temperature of your sample drop closer to room temperature, though anything below around 80F should be fine. The only exception to this is the chlorine test since the chlorine tends to outgas relatively fast from the vial so that should be tested right away. The only test that is very temperature sensitive is the CYA test since it's a turbidity test, but for best results let the sample cool for the TA and CH tests. For the pH test, you can try this both ways -- in theory if the chlorine outgassed (before you add the indicator dye since it contains some thiosulfate which would get rid of the chlorine) the pH should rise a bit, but at normal levels even 4 ppm FC outgassing would only raise the pH by 0.05 units so I suspect that this effect isn't measurable (so don't worry about it).

Richard

[Emprov]

You can just air dry them after rinsing them out with tap water (or filtered water, if you've got that at the sink). I'd leave them uncapped, however.

You should generally let the temperature of your sample drop closer to room temperature, though anything below around 80F should be fine. The only exception to this is the chlorine test since the chlorine tends to outgas relatively fast from the vial so that should be tested right away. The only test that is very temperature sensitive is the CYA test since it's a turbidity test, but for best results let the sample cool for the TA and CH tests. For the pH test, you can try this both ways -- in theory if the chlorine outgassed (before you add the indicator dye since it contains some thiosulfate which would get rid of the chlorine) the pH should rise a bit, but at normal levels even 4 ppm FC outgassing would only raise the pH by 0.05 units so I suspect that this effect isn't measurable (so don't worry about it).

Richard

Looks like I stand corrected by someone with vastly superior knowledge on the subject.

[chem geek]

Emprov, you weren't wrong. I probably wasn't clear or I misinterpreted. By "air dry" I mean just let it dry out on its own. You don't have to actually blow air into it to dry it out. As long as you rinse the vials out, you can put them in the case as is -- with the caps off. They will dry out on their own before the next use and even if they don't you should always just rinse them again before use.

In any event, waterbear knows testing far better than I, but I've never heard of any test errors due to not drying out the vials. Not rinsing them out, yes, that has caused problems, especially between two tests done in sequence (and don't forget to rinse the cap).

[Emprov]

Emprov, you weren't wrong. I probably wasn't clear or I misinterpreted. By "air dry" I mean just let it dry out on its own. You don't have to actually blow air into it to dry it out. As long as you rinse the vials out, you can put them in the case as is -- with the caps off. They will dry out on their own before the next use and even if they don't you should always just rinse them again before use.

I was referring more to the temperature thing. In my long history of owning a spa (going on 4 months now?), I've always assumed that testing at spa temperature was the way to go. Knowing a bit of what happens to chlorine (as you pointed out), I assumed that the other chemicals may react similarly and, that the water should be tested as close to real life spa conditions as possible, i.e. same temp. You've piqued my interest on this.