Aquarium Water Change Calculator

A common guideline is a 10 to 25 percent change every week or two for a stable, stocked tank, with larger changes to correct a problem. The right amount depends on stocking, feeding and filtration, so treat any single number as a starting point, not a rule.

The tool uses the exact conversion of 1 US gallon to 3.785412 liters. So a 13.75 gallon change is about 52.05 liters. If your tank is rated in liters, divide by 3.785412 to get US gallons before entering it.

Use a realistic net volume. Gravel, rock, sand and equipment displace water, so the actual volume is often 10 to 15 percent below the rated tank size. Entering net volume keeps the change amount honest and avoids overdosing treatments.

Frequent partial changes dilute waste while keeping temperature, pH and hardness stable. A single very large change can swing those parameters fast and stress fish, so most keepers prefer smaller, regular changes over occasional big ones.

Yes. Match the new water to the tank temperature and dechlorinate tap water before adding it, since chlorine and chloramine harm fish and beneficial bacteria. This tool only sizes the volume, so follow your normal conditioning routine.