Clearer, Less Distortion, Lighter, More Shapes, No Brackets, Better Insulating Read More...
Compared to glass tanks, acrylic tanks
Are Lightweight And Crack Resistant
Make It Easier To Cut Holes Into To Accommodate Plumbing
Acrylic Distorts Much Less And Is Clearer Than Glass
Provide Better Views Because Of Curved Front Corners
Come In Many Interesting Molded Shapes
Provide Much Better Insulation
In terms of weight, acrylic tanks beat glass tanks hands down. Acrylic tanks are about half the weight of their glass counterparts. Acrylic tanks are more crack resistant than glass and easier to modify. Acrylic tanks will resist knocks and drops much better than a glass tank could ever hope to. Acrylic tanks are far easier to cut than glass tanks are should you want to customize your tank to accommodate plumbing. It's not impossible to cut glass, but you just need to have special tools and know what you're doing. Some of the larger glass tanks are made out of tempered glass. This glass cannot be cut outside of a factory.
Acrylic lends itself to more interesting shapes because of the way it can be molded. Acrylic tanks come in hexagons, pentagons, bull noses, columns, waves, etc
with minimal seams and no metal bracing. If you require an aquarium with a height in excess of about 30 inches, Acrylic is clearly the way to go.
Clear acrylic panels have almost the same refractive index as seawater so there is no bending of light as it passes from the acrylic into seawater, providing brighter color and sharper shapes in acrylic aquariums. The huge viewing windows in large public aquariums can are made of acrylic, they afford a very clear view of the water and ocean life. Acrylic also allows better penetration of your system lighting, which is especially important for reef systems.
Acrylic is a better insulator than glass. This may not matter if you have cold water fish but if you're keeping a tropical tank, you probably want to consider this factor. Acrylic tanks can retain heat 20% better than glass tanks. Acrylic aquariums will usually cost more than glass tanks for the same size, but the benefits, the aesthetics, and the long term maintenance free ownership, far outweigh the cost differential.
Another issue that brought up over and over with acrylic tanks is that they are easily scratched by cleaning objects or gravel. As long as you're careful when you're cleaning the tank, you should be okay. But should a scratch occur on your tank, you can simply buy scratch remover kits that do a fine job remedying the blemishes.