Water Change Calculator
Work out how many litres to change to hit your target percentage.
How it works
Water to change (L) = Tank water volume (L) × (Percentage ÷ 100). To dilute a parameter, required % change ≈ (1 − target ÷ current) × 100.
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Formula & Method
Water to change (L) = Tank water volume (L) × (Percentage ÷ 100). To dilute a parameter, required % change ≈ (1 − target ÷ current) × 100.
Example Calculation
For a 40% change on a 60 L tank: 60 × 0.40 = 24 L. To halve a nitrate reading you'd change about 50% of the water.
Frequently Asked Questions
How much water should I change weekly?
For most community tanks, 20-30% weekly keeps nitrates in check. Heavily stocked tanks may need more.
Should I match new water temperature?
Yes, always dechlorinate and temperature-match replacement water to avoid shocking fish.