How Much Evaporation Is Normal For A Fish Tank?

How Much Evaporation Is Normal For A Fish Tank? A 40-gallon tank will evaporate about 1⁄2 gallon per day, give or take. That means you need about 3.5 gallons of purified freshwater per week. How do I stop my fish tank from evaporating? Air Movement Evaporation slows down as the humidity in the air above