Quick take
Size the sulfur filter from both household peak GPM and available backwash flow. A system that cannot clean its media properly can disappoint even when the chemistry is otherwise correct.
Confirm the odor source first
Hot-water-only sulfur odor can originate in the water heater. If both hot and cold well water smell, source-water hydrogen sulfide becomes more likely.
Service-flow sizing
For smaller homes, 12 GPM-class systems are common. Larger homes with heavy simultaneous use can justify 20 GPM-class equipment.
Backwash sizing
Sulfur/iron media requires sufficient cleaning flow. Check the filter manual against the actual pump output available at the installation pressure.
Test related chemistry
Iron, manganese, sulfur and pH often interact. Test all of them before selecting media and tank size.