OTO and CYA and TC, oh my! What's being measured?

[aquarium]

OTO is just measuring your TC. If the CYA is low then your FC will be burned off by sunlight. If you monitor the FC throughout the day you can see the effect. It is the FC that is the sanitizer.

Thanks,

I guess that's the heart of my confusion. How does CYA work? Does it take the chlorine -completely- out of service, and out of detection by the OTO test kit, or does it just release it more slowly in the presence of sunlight? In brand new fresh water like I now have, it's doubtful there is any CC, so TC=FC?

TW