Is it possible to calculate ORP based on your pool test results?

VinceL · Apr 12, 2015

This will be our 3rd full summer for our fiberglass pool. I have the Hayward Sense & Dispense. Each spring I have had to make a minor recalibration adjustment to the pH sensor (typically .1 - .2) after doing several tests. In past springs, the ORP sensor gave what seemed like reasonable readings based on FC, pH, CYA, TA, and temperature. This year I am skeptical of the ORP readings I am getting. So, I am wondering if the ORP sensor could be going bad.

Are there any specific symptoms that would indicate the ORP sensor is going bad? Does it just stop giving readings? Does it get stuck on one value?

Also, if I have all my pool readings (like I mentioned above), is it possible to calculate what the ORP is? If it is complex math (too many years since calculus :scratch:

), are there charts which show ORP based on pool readings?

Patrick_B · Apr 12, 2015

Very theoretical compared to reality, and it never equates to FC accuartely. That is the very short answer from many years of field experience.

JasonLion · Apr 12, 2015

Those sensors are normally replaced every two years.

VinceL · Apr 12, 2015

JasonLion said:
Those sensors are normally replaced every two years.

Geesh....the probes are something like $280 and they only last a couple of years.

I can buy a whole new Sense and Dispense for a little over $500. That would give me new ORP and pH probes for less than buying the 2 probes by themselves. Seems kind of crazy.

JasonLion · Apr 12, 2015

Just one of several reasons we never recommend using ORP sensors with residential pools.

Patrick_B · Apr 13, 2015

In all honesty, ORP and pH sensors can be very finicky and they are replaced annually as best practice for industrial applications. Even when used in clean water systems.

parched · May 21, 2015

I have a pH/ORP Technopool controller, and had to chime in esp. regarding probe costs. The Technopool is made in Italy, so I really quickly found USA sources for almost everything it expends. Oakton and Extech plastic-body pH probes start at $30 and ORP probes start at $50 on Amazon; you may get one that has 4-6 mo of shelf life gone but at that price I replace mine annually anyway. I donate the old ones to a local school and they'll get another 6-12 months out of them. I did also quickly note that the pool supply places cheerfully charge you 4x-6x or more. The Santoprene peristaltic pump tubing is available by the yard at US Plastics, as are Kynar/Viton check valves (replaces duckbill foot valves). I spend maybe $100/yr and replace everything the chemicals touch. I do agree that other factors, esp. any other chemical you may add, can change the ORP reading. I think I have good luck with ORP control because the pH is also regulated, and I use liquid chlorine not an SWG. I keep a high-ish CYA of about 50; I'm in So AZ so I run my solar heater at night to keep the water <90F in summer. I just set my ORP to maintain 5-6 ppm FC (per my test kit) in the late afternoon after max sun exposure and I don't seem to have algae issues. I calibrate the ORP probe with a bleach solution and it basically only needs have enough life to respond to that above 800mV, since I'm not using it for precise readings. If/when the controller takes a lightning strike I may try the Arduino approach I saw in the forum. I like the ORP control because previously it seemed like I was adding chlorine every couple of hours in summer even at higher CYAs. Good luck (& shop around)!