Water changes are kind of up to you, how many people using it, how you doing on chem balance and possibly any water restrictions? Every 4 months is a rule of thumb but some do it more, some will go twice a year. As far as the bulb the spa will tell you when a year has passed by a blb error on your topside, looks like a 616 though. I tell people to go a year and a half and it's not been an issue.
