As Europeen I am not very familiar with what a gallon is in litres. I do find two different conversion factors depending on if we talk about gases or fluids.
Why do I ask?
Several on this and other forums write that they convert a 30 gallon aquarium (holds water, fluid) or use a 30 gallon terrarium (holds air, gas) and these should not be the same size in volume! Or do I miss something?