Estimate the water change needed to dilute nitrate toward a target level.
Open live calculator →Reducing 40 ppm toward 20 ppm requires an idealised 50% water change if replacement water contains no nitrate.
Idealised single-change estimate with complete mixing.
Model a single idealised water change from current nitrate, target nitrate and net aquarium volume.
The live tool updates immediately and shows the result in the units commonly used by aquarium keepers around the world.
Test both aquarium and source water.
The model assumes complete mixing.
Large or urgent changes should follow livestock-specific expert guidance.
Many freshwater keepers aim below 25–40 ppm, planted tanks often sit lower, and sensitive reef systems typically target under 10 ppm. Species-specific guidance takes priority over general rules.
The model assumes perfect mixing and nitrate-free replacement water. If your tap water contains nitrate, or detritus keeps producing it between measurements, the real drop is smaller—test your source water.
Chemically a single 50% change dilutes more than two 25% changes, but several spaced changes are gentler on livestock. For high readings, do moderate changes over consecutive days rather than one extreme change.