Hello and thank you for your inquiry.
RO membranes should be changed out about every 1-2 years, but can be extended to 2-4 years by using a flush valve.
Metal halide bulbs should be changed every 9-18 months depending on the type of ballast used and they type of bulb. On average if you change them about once per year that should be fine.
If there is anything else we can do for you please let us know.
Marine Depot Customer Service