Find your disinfectant first
Check your utility CCR or water-quality page rather than trying to infer disinfectant from smell.
Do not buy carbon by tank size alone
Compare the specific reduction claim, service flow, media volume, expected life and pressure drop. If your concern is only drinking water, point-of-use treatment may be more economical than whole-house treatment.
Next step
Run your numbers through the Water System Planner, then verify any product against its actual service-flow, pressure-drop, capacity and certification data.