IMHO, pH controller is not a must hv, but it is a good to hv as it makes ur job of tuning the CR easier. It also safeguards against too low a pH, preventing pH crash in main tank, etc.
it is best that the CR u r getting comes with a pH probe attachment to slot in the probe into the CR. that will give u the exat value of the pH in ur CR and from there, u control ur pH.
check out the below-mentioned,
Local sponsors: Coral Labs, I-Aquatics, Reef Maniacs
Foreign makes: Deltec, Korallin, etc.