There's a lot more to this question.
What corals are you planning on keeping?
What filtration are you using/planning on using?
How often are you doing wc's?
Are you using ro/di water?
How heavy do you plan to feed?
I'm at 28 fish in a 120 DT but total system water volume is slightly over 200gals. I currently do 5% wc's weekly then once a month I do a 10-15% wc
It all depends on how much work you're willing to do to maintain your water quality. Also if you plan to run bio pellets or gfo or a fuge?