What is the difference in this, and the 55 Gallon Aquarium I can buy at my pet shop for ~90.00 on sale?
Not being ignorant...I really don't know.
This is a custom made one that is reef ready, reef ready means that it is ready to have plumbing to accommodate a sump below the main tank somewhere, a sump is used to hold most of the equipment and possibly a refugium(a different type of salt water ecosystem with macro algae etc.), so the main tank can look cleaner and prettier. Also the pvc bottom rather than a glass bottom makes the tank less likely to shatter due to rock movement. Starphire glass on the front of the tank is a more clear type of glass. This one is also rimless which gives the tank a cleaner look to it. Yes there are cheaper aquariums, that would probably work well depending on what your looking to do with the aquarium, but this one is a high quality and custom made.