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.