ORP information question

[firstone]

Disclaimer: I do not use ORP to control anything. It's strictly for my information.

So, I bought this Wi-Fi Ph/ORP tester from aliexpress mostly because I'm interested in anything related to home automation. And later replaced probes with atlas scientific (consumer) ones. It seems to show Ph pretty accurately. But ORP mostly stays in 450-500 range. Rarely going as high as 600. While I'm reading that in commercial pools 650 is a minimum.

It's SWG pool with higher CYA (60), which I understand would affect it. Just curious how. Everything mostly fine with my water, both, chemically and visually. FC is in 2-3 range, CC is .2-.4 range. Not sure if the latter is bad? Ph is pretty stable in 7.6-7.8 range.

 

[JoyfulNoise]

The ORP probe is sensitive to all kids of redox chemical reactions as well as pH and sunlight conditions. The one thing you would want an ORP probe to be sensitive to is the hypochlorous acid (HOCl) concentration as that is the primary oxidizer and sanitizer in water. However, cyanuric acid is a chlorine buffer meaning it captures most of the chlorine and holds it in reserve. That results in very low levels of HOCl which is fine for sanitation and oxidation but is often too low for an ORP probe to be useful. So it’s basically a signal to noise problem - lots of useless noise with very very small signal embedded into it.

Outdoor pools absolutely need CYA and an SWG tends to need higher levels than a manually chlorinated pool. If you didn’t use CYA with your SWG, then you’d have to run it at 100% output all the time which would reduce its lifespan greatly.

 

[firstone]

Thank you. Not an answer I wanted to hear but makes perfect sense.

 

[JoyfulNoise]

ORP probes also use a very thin glass membrane that is conductive to ionic species and connects the internal electrolyte to the solution being measured (salt bridge). There is also either a noble metal (platinum or gold) band or wire that is immersed in the water (measurement electrode). The membrane and noble metal electrode can both become fouled with contaminants in pool water. This can cause the ORP voltage to read incorrectly. There is usually cleaning instructions with most probes that describe how to gently clean the surfaces for optimal performance. Some probe makers even suggest using toothpaste to clean the probes. Cleaning the probe is generally a monthly task or whenever it is suspected that the probe might be fouled. ORP probes generally need to be replaced every 18 months or so depending on use.