PH Probe A/D Coverter ?

[skimask]

My next question is can I raise Vref- above ground, say 1.33v or does vref have to be ground.

Yep, you can put Vref- to anything you want (>Vdd not included )
If your crafty enough, you can even use a couple of the PICs pins to make an R-2R ladder so a guy can even vary Vref+ and Vref- to suit the conditions. (i.e. read 0 on the A/D, lower Vref-, read 1023 on the A/D, raise Vref+, and so on...)