As the title says.... if your tank is only 30% stocked by your estimate, could you do less water changes? If your useful schedule is one water change per week for a 100% stocked tank, could a 30% stocked tank be every 2 weeks?

I like to err on the side of caution but you probably could if your filtration is good and if you monitor the aquarium well. Should probably wait for more replies though, see what others have to say.