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?
Since corals actively pull out nitrates(1), ammonium(2) and phospahtes(3) to feed their Symbodinium spp. dinoflagellate symbionts arguably they can be considred part of the fitlration. One thing you need to take into consideration is how big the fish are going to be in 3 - 5 or more years, the time it takes for many fish to mature like dwarf angels and tangs (some which may take longer than 5 years) to mature. Do not go by the totally bogus rule of thump of so many inches per gallon!