Does orthotolidine test include Combined Chlorine?

Ronald U.

Bronze Supporter
Am I understanding correctly that Orthotolidine colorometric test gives me Total Chlorine (FC + CC)? That would explain this morning's results:
Ortho. Chlorine Test 3.5
FC 2.0
CC 1.0
TA 90
CH 300
Borate 40
CYA 40
Thank you. Regards.


TFP Expert
Platinum Supporter
May 23, 2015
Tucson, AZ
The OTO test typically develops its full color over time. The initial color you'll see is FC and then it darkens to give you TC. I don't use the OTO chemistry because I have never gotten accurate results from it. It's best to think about it as a "presence of chlorine" test than any kind of accurate measure.