Testing with high TC

[polyvue]

CYA
Taylor doesn't talk about this, but it seems that chlorine bound to CYA does not form the melamine-cyanurate precipitate which means that the CYA test will read artificially too low when the FC is high. This should be able to be handled by adding around 2 drops of R-0007 thiosulfate to the water sample for every 10 ppm FC before you add the CYA reagent.

It would be interesting to test this with FC levels of 20, 30, 40 PPM... both with and without the thiosulfate.

[waterbear]

You all forgot one test that is affected by high chlorine levels...all DPD chlorine tests (comparator is shades of red/pink) (and to a lesser extent FAS-DPD tests).
They can "bleach out" and remain colorless at high chlorine levels (DPD over 10 ppm FC and FAS-DPD over 25 ppm---but are usable at higher FC levels with certain modifications.)
If your chlorine test is reading low and you suspect there is chlorine in the water (expecially if you saw a pink flash before the DPD test turned clear) do an OTO test (comparator is shades of yellow). It is a foolproof test that will ALWAYS tell you if you have chlorine (or bromine) present.
If it turns yellow to deep yellow it's most likely swimmable, if it's deep yellow to orange you are most likely shocking, if it's orange to brown stay out of the pool but throw in the whites because you have a pool of bleach!

[giroup01]

When testing high levels of chlorine with DPD, add the DPD1 and DPD2 in the empty test cell then add the sample water slowly - it should turn pink, then red then clear as more and more water is added. You can determine that way if you're in a 0 TC or high TC situation.

For CYA there was an article by Woto in the JSPSI describing the interferences of CYA with high chlorine, as I recall he does mention to add a few drops of thiosulfate to the sample water. I'll have to find the article.

And with the ProTeam borate titration, a high TC level bleaches out the indicator.

[waterbear]

And with the ProTeam borate titration, a high TC level bleaches out the indicator.

Which is why I usually use the LaMotte Borate strips! The color change in the Proteam indicator is just plain hard to read, bleachout or not! If memory serves correctly it is bromphenol blue. I do use the Proteam titration kit when I need to make adjustments to the borate levels (perhaps once a year) but the strips are good to tell me I am in the 'sweet spot' of 30-50 ppm!