How much does a gallon of saltwater weigh?

A gallon of saltwater weighs approximately 8.5 pounds. People planning to install a saltwater fish tank should use an average of 10 pounds per gallon when trying to determine the weight of the fish tank.

The additional 1.5 pounds factored in when determining the weight of a saltwater fish tank takes the weight of the rock, tank, stand and other accessories into account. For larger fish tanks, it is important to determine if the floor where the fish tank is placed can hold up to the total weight of the fish tank once it is full of salt water and fully decorated.