What Is the Volume of Water in a Fish Tank in Liters?. Part of the series: Geometry Tips. When measuring the volume of water in a fish tank, you'll want to do so in liters. Find out how to solve for the volume of water in a fish tank in liters with help from a longtime high school math tutor in this free video clip. Read more: http://www.ehow.com/video_12215103_vo...