Why does pH affect salinity?

[Orcrone]

I calibrated my pH probe & as a result my pH is now reading 0.1 lower. At the same time my salinity started reading about 1.3 ppt higher. The pH probe is in the sump & the salinity probe is in the DT, so I never came near the salinity probe while calibrating pH.

 

[kurt_n]

The two shouldn't effect each other as far as I know. Might be just a coincidence?

 

[reefjunkie42]

+ 1 for what kurt_n said

 

[Orcrone]

The two shouldn't effect each other as far as I know. Might be just a coincidence?

Doubt it. Salinity was holding for a long time with a 0.2 ppt swing total. When you graph pH & salianity there is a discrete jump in salinity by 1.3 ppt at the exact time pH dropped due to calibration. It's held there since then.

I don't think there's a physical relationship between the two, just some property of the Apex.

 

[swearint]

Keep in mind that you are not actually measuring the salinity, you are measuring conductivity and inferring salinity. From what I could find on the internet, extreme values of pH will influence conductivity. Since you merely calibrated the pH probe, the actual pH is unlikely to have changed. I don't know if the Apex uses a pH correction factor in conductivity. Conductivity is strongly influenced by temperature though.

Todd

 

[Orcrone]

Keep in mind that you are not actually measuring the salinity, you are measuring conductivity and inferring salinity. From what I could find on the internet, extreme values of pH will influence conductivity. Since you merely calibrated the pH probe, the actual pH is unlikely to have changed. I don't know if the Apex uses a pH correction factor in conductivity. Conductivity is strongly influenced by temperature though.

Todd

I agree. If I calibrated the temp probe I could understand the change. pH wasn't extreme. Went from reading 8.41 to 8.31 after calibration.

 

[schwaggs]

The only thing I can think of is a bug in the calibration routine. Seems unlikely, however. I would email the details to Curt to see if he has any ideas.

 

[Orcrone]

Good suggestion. Just sent Curt an e-mail & attached a portion of the data log.