There are many advantages and disadvantages to both glass and acrylic aquaria. With glass, the larger the tank is, the thicker the glass has to be - and so it becomes heavier. With acrylic this is not the case, and large aquria can be made from thin, light acrylic. Acrylic does scratch more easily than glass, but acrylic isnt as affected by these scratches as glass is - with glass they are disasterous as they create a weak point in the aquaria, with acrylic this is not the case, and scratches do not weaken the aquaria. Glass is clearer than acrylic, and acrylic tanks can begin to let off a slight smell after a while. Acrylic tanks can be made into many more different and interesting shapes to glass tanks, which have their limitations. And acrylic is cheaper...
Thom.