Fas DPD Test residue

[H2O_Keeper]

THroughout the season I have used the TF100 FAS-DPD test quite a bit. There is a black film that has formed on the vial and I was able to get most of it off with just water and wiping it down good. It still looks stained. I have the same black residue over the spoon for powder.

Can I use MA or something else safely to remove this residue (more concerned about the spoon being dissolved)?

What is turing things black?

 

[duraleigh]

A solution of 3:1 water to muriatic acid will clean about 98% of it. It's the nature of the beast.

 

[PaulR]

Seems to me I read that straight bleach would also clean it up. I use the cylinder for dosing my spa (usually 10-30ml of 12.5%) maybe that's why I've never observed the problem, despite using FAS-DPD twice a day for the past six months or so.
--paulr

 

[Pisces]

I was getting a residue buildup...cloudy looking...so I filled the testing vial with straight 6% bleach and let it soak for a half day or so. Read about it on another thread, with an explanation of why this happens. Cleared it up again. Now I'm rinsing the vial well after testing and wiping it dry inside with a clean paper towel. It's stayed clear since then. HTH.