When adding new water, it's also important to use a water conditioner to remove any harmful chemicals. It is also recommended to match the pH and temperature of the new water to that of the existing tank water.
Do you let new water sit before put it in the fish tank?
Yes, it is generally recommended to let new water sit for 24-48 hours before adding it to a fish tank. This allows time for the water to dechlorinate and reach the same temperature as the water in the tank, reducing stress on the fish.