ORP question


Gold Supporter
In The Industry
Apr 22, 2019
Homer, AK
I just got my Hanna HI98121 yesterday along with bottles of calibration, cleaning and storage liquids. My pool is kept at 95 degrees and receives heavy use. They recommend that the PH function be calibrated every time I use it and they also say that after calibration, I should just put the probe in the actual pool water so the temperature is accurately recorded. Hanna claims that PH is temperature dependent and unless the temperature is known the reading is not meaningful. I ran my first test this morning and got ORP of 735 and PH of 7.55. The water is very clear and has no chlorine smell at all. The users are very happy with it. I'm just wondering if anyone has an opinion about these numbers? Is an ORP of 735, PH of 7.55 at this temperature considered good, OK or something else? Performing the test has to be done on my knees so the probe can be put in the pool water right after calibration. Also, the numbers take a few minutes to stabilize. They have a little clock on the screen and they say to keep it in the water until the clock disappears. It's really pretty easy to use. I'll post a photo of it from my phone.


Silver Supporter
LifeTime Supporter
Oct 5, 2007
Valrico, FL
Your pH meter is temperature compensated. That means the instrument reads the water temperature and applies a correction to the reading. So if you have properly calibrated your meter, the pH reading is correct. As far as ORP goes, it depends on how much stabilizer (CYA) you have in your pool. if it is more than 30 ppm, the ORP reading is useless.
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