it depends on what equipment you're running and what you're feeding and how often.
i have a 12 gallon back home. i change 1 gallon a week but i feed very little. that tank has been going strong for more than 2 yrs. i think most people would say 1-2 gallons a week
i am using emperor 400 as the filter, 25w heater, 1 pvc pipe for hiding.
i added the pair o.clownfish and 2 shrimps on tuesday.
also feeding once per day
so, 10 % water change every week will be fine?