CYA and ORP

[Aqua Lab Rat]

OK, this has bothered me for a long time. Does CYA actually interfere with ORP sensors, or is the sensor giving a true indication that most of the chlorine is bound to CYA and not truly "free"? My inclination is toward the latter one but I don't have enough experience with them to know.

 

[splashpad]

@Aqua Lab Rat, I like this article (jsut found on search) https://www.poolspanews.com/how-to/maintenance/understanding-orp-and-ppm_o

Based on that article I would say the PH has "more" effect on the readings (which is true, higher PH does slow chlorine's reaction), then CYA (depending on the time of day of the reading)

 

[ajw22]

Problem is that an ORP sensor does not know how much CL is bound with CYA that can be freed as needed. So an ORP system with high CYA will think that CL is low when it is not.

An ORP system cannot work as designed with high CYA levels.

 

[Costas > DownUnder]

A couple of older threads worth reading on this topic....

We don't recommend ORP

CYA level when running SWG and ORP probe

 

[dschlic1]

From my experience, if CYA is over 30 ppm, then the ORP will not change in a meaningful way even with very large changes in FC. Below 30 ppm, ORP is usable for regulating FC.