AGA Fluorescent Black Hexagon 20 Gallon Hood Our most popular Hood is designed to perfectly compliment your All-Glass aquarium. It is custom fit to sit on the inside lip of the aquarium frame, which greatly reduces evaporation. They are designed to fit all major brands of aquariums. The Hood is for 20 gallon tank that sits inside the frame of the tank which is 18 inches Our most popular Hood is designed to perfectly compliment your All-Glass aquarium It is custom fit to sit on the inside lip of the aquarium frame, which greatly reduces evaporation They are designed to fit all major brands of aquariums Our most popular Hood is designed to perfectly compliment your All-Glass aquarium It is custom fit to sit on the inside lip of the aquarium frame, which greatly reduces evaporation