Just wondering if there are any PHREEQC users here. I've been working on calculating LSI (Langelier Saturation Index) based on the output from PHREEQC (pHs), and based on LSI = pH - pHs. In theory, it appears that the SI (saturation index) from PHREEQC should be the same as LSI, but it is not the case, and I'm wondering what went wrong. The pHs predicted by PHREEQC is different form the pHs predicted by empirical equations. If anyone has any experience in this, I would be most interested to hear from you.