A worked example
A 30% change in a 60 L tank
- Start with
- 60 L · 30% change · conditioner 5 mL per 200 L
- Check the result
- 18 L replacement water · 0.45 mL conditioner
Follow any separate dosing instructions supplied with your product.
Everyday tool
Aquarium Water Change Calculator
How much replacement water and conditioner should you prepare? Calculate from actual volume, change percentage, and the product label.
Conditioner is calculated for replacement water; check the label first
Plan a water changeCalculate replacement water, conditioner, and a temperature mix.
Calculate tank volume first →Water change settingsUse actual water volume, not gross tank size
Water conditioner labelEnter the dose printed on your product
per
Temperature mixing
Water change result
30% water change4.5 galreplacement water
Water remaining10.5 gal
Conditioner0.5 mL
Changes per month4.3 times
Monthly water use19.6 gal
Temperature mix for replacement waterCold 2.3 gal + Warm 2.3 gal
Estimated mix for 77°F
Always follow the conditioner label. Mix water in a separate container and verify temperature with a thermometer before adding it to the tank. Never pour hot tap water directly onto livestock.
Water-change preparation
Check replacement volume and temperature mixing
Work out the replacement volume
Enter actual tank water and the change percentage. Adding an interval also estimates average monthly water use.
Scale the label dose
Enter the product’s stated mL dose and water volume. The result applies to replacement water, not the entire tank.
Mix cold and warm water
Enter both temperatures and the target to see mixing amounts. The target must lie between them; verify actual temperature with a thermometer.