Water Change Calculator

Project nitrate/phosphate reduction across water changes.

This calculator estimates how water changes reduce nitrate (NO3) and phosphate (PO4), how many changes it may take to hit your targets, and what your levels may look like over a planned schedule.

System water volume (gallons) Water change size (%) Current nitrate (NO3, ppm) Target nitrate (NO3, ppm) Current phosphate (PO4, ppm) Target phosphate (PO4, ppm) Replacement water nitrate (NO3, ppm) Replacement water phosphate (PO4, ppm) Planned number of changes (projection) Days between changes

Formula used: after each change: new_level = current × (1 - change_fraction) + replacement_water × change_fraction
Assumes no additional nutrient input/export between changes.

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