Nursery pond, or rearing pond, water should be changed every one to two weeks with the use of a filter. A pond will need to be changed more often if a filter isn't used between cleanings. In designs without constant filter-use, daily changes of around 10% may be required. When changing water on a weekly basis, between 10% and 15% of water should be removed, and clean water added.
If your pond is exposed to the elements, it'll lose water naturally through evapotranspiration. Once around 10% of the total water has evaporated, fresh water can be added.
