So, it just freezes the PH at where ever it is when you tell it to ‘control’? I suspect thats how most of them work. Or maybe they just get it back into the set range when it goes out of range?
I really like the idea of having the PH move through a range that you can select - but under control.
From the little I know about programming, I dont think that will be all that difficult. <<<<< hehehehe I just realized what I said after all that crap I went on about above!! 
Ive been looking into this more, and I think you are right about the PH shield. It looks like that is the gizmo you need to convert the analog voltage from the probe into a digital format that the controller can use.
I have an Uno, but I have no clue if it can do what I want. I cant even remember why I have it. Its been several years since I messed with it. At the time I was trying to customize an altitude/GPS in-flight data logger I had for my models. I think I needed to use it to program the data logger?
I have not found any tutorials that were just for a PH controller that were simple enough for me to follow or use. @Northern_Loki posted some links above, but they are all far more ambitious than what I want or need, and I have no clue how to take the bits I need and separate them out.
Do you have any links to something that might be better?
I know we arent the only ones. If we can come up with something workable, Im betting a bunch of folks will be real happy.