The standard is normally the "ISRM Pool Plant Operators Course". "The course is designed for supervisors and managers who are responsible for safe swimming pool operation. It provides core knowledge including pool water testing and current COSHH requirements". I completed this many years ago and was completed within 3 days. The course consisted of a basic exam and coursework that required to be submitted. Its useful for anyone whose responsible for pool management in regard to the leisure industry. Once completed you will never swim with your mouth open :)

Try PPL training. I did a slightly different course on legionella risk assessments to City and Guilds standard and would highly recomend them