Aquarium Water Change Calculator
See how much water to remove for a partial water change. Enter the size of the tank and the share you plan to change.
- Free
- Works offline after your first visit
- Saves on this device
- No sign-up
- Updated
How it works
Multiply the tank volume by the share you change. Many keepers change part of the water on a regular schedule. The right share depends on the tank, the fish and the filter.
Replace the water with new water that matches the tank's temperature, and treat tap water first as your supplier or store advises.
Worked example
In a tank that holds 20 gal, changing 25% of the water means removing 5 gal.
Questions
How much should I change?
Many keepers change a fraction of the water every week or two. The right share depends on the tank and what lives in it.
Should I use cold tap water?
No. Match the temperature of the tank as closely as you can, and treat tap water first.
Does the filter's water count?
No. This counts the tank volume you enter. Filter and plant water add a little extra.
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