We have an ozonator. Our spa is 360 gallons. How much sanitizer should be used each week - normal bather use?

There is no fixed amount of sanitizer to use. Sanitizer requirement will depend on a number of factors including frequency of use, number of bathers, contaminants from bathers such as body oils, soap residue, perfumes, etc. RECOMMENDATION: keep the sanitizer level at the recommended parts per million. Yes, you will likely use up your chlorine less often with the aid of an ozone generator. RECOMMENDATION: mix in a tablespoon or so of Spa 56 right after you use your hot tub. That way it can "go to work" on what you have left behind in your water.