I've often received questions about the differences between high-clarity low-iron glass tanks and normal glass tanks, so for those who are new to the hobby... here is a visual comparison for reference.
The tank on the left is made from normal "float" glass, it has a noticeable greenish tint. The tank on the right is made from high-clarity low-iron glass and looks almost clear.
High-clarity low-iron glass tanks are sometimes also labelled as "crystal" or "optical" glass. The light transmission for this type of glass is much higher, which results in brighter light perception and more accurate color rendition when viewing the tank.
Here is a close-up look at both tanks side-by-side...
So the next time you go shopping for aquarium tanks, do keep a look out for such tanks... their price difference may not be as wide as you think, and it may be worth just going for the high-clarity ones. :)