This paper details the development of a wearable Cl^- ion-selective electrode for use in cystic fibrosis patient monitoring. Ag/AgCl electrodes were adapted with a Cl^--saturated poly 2-hydroxyethyl methacrylate (pHEMA) hydrogel mixture to act as a reference electrode. The length of time which the pHEMA was conditioned in the solution, as well as the concentration of the conditioning solutions were variables examined during the development of the device and compared to the conditioning process of similar devices from literature. In contrast to other studies, it was found that a 3M KCl condition did not produce a stable Cl^- concentration within the gel. Instead, conditioning the pHEMA in a 1 M KCl solution for 25 hours produced electrodes which exhibited strong sensitivity toward the Cl^- concentration of test solutions, over a range of 1 mM^-1 M. The electrodes demonstrate sufficient stability that plans are in place to conduct a healthy volunteer study to examine their efficacy whilst placed on the skin of participants.