Ph calibration accuracy at low range when using high calibration points

[Gabaghoul]

Setup my new Geo’s Reef 818 last night and she’s been running for a day now. No leaks. I wanted to start adding CO2 after calibrating my new dual junction pH probe. Of course, I don’t have 4 solution on hand but I do have plenty of 7 and 10 so I ordered some from BRS. It won’t be here until next week.

My question is this. How inaccurate will my probe be at low range(6.5-7.5) if I calibrate using the higher point calibration solutions 7 and 10 until I receive the 4 solution next week?

 

[cypho]

For that range (centered right around 7) 7 and 10 is just as good as 4 and 7. After all, 7.5 is closer to 10 than it is to 4.

But to answer your question, my pH probe is calibrated with 7 and 10, and it is off by around 0.1-0.2 at pH=4

 

[Gabaghoul]

Thanks. I think I can work with that and then when I get the 4 solution next week I can recalibrate. .2 error all the way over at 4 doesn’t seem that off. It’s probably much more accurate around 6.5 or 7 from what you’re seeing.