This was probably the first major thing I learned about aquariums when I started researching all the options. Go glass.
Glass is better in most cases – Here is where it isn’t
I want to start with the disadvantages of glass. Glass is heavy. Much heavier than acrylic. This is typically not a huge disadvantage as the majority of the weight from a tank comes from the contents. Water weights 8.5 lbs per gallon. A 100 gallon tank weigh 850 pounds in water alone. Never mind the sand, rocks, equipment, stand, sump, tank and everything else. To me, the weight advantage of acrylic is meaningless for this reason.
Glass is only available in limited shapes. If you want a tank the shape of a doughnut, you will have to go acrylic. Part of the reason for that is glass is much harder to fabricate. In a previous post I mentioned that I am designing my own sump. I actually will not be constructing the tank itself (buying a pre-built) or cutting the baffles. I am having all that done for me. I am just assembling the sump.
Durability: Scratching vs Strength
Acrylic is easily scratched. The primary issue with that is cleaning a tank can be very abrasive. Even if you use acrylic friendly soft cleaning material, sand or other objects in the tank can get caught in your cleaning tools. If you rub sand against an acrylic tank, it will no longer be clear. In fact, acrylic looks scuffed and old very easily.
Acrylic is, however, very strong. A properly built acrylic tank is almost impossible to break. Even the strongest glass (tempered and thick) will break under various types of stress. Even the acrylic seams are more like welding than sealing. Basically, if you need to put your tank in a rocket ship or other location where physical stress is common, then acrylic may be your material.
Glass will not easily scratch. In fact, cleaning with a razor blade is routinely done in glass aquariums.
Working with the materials
I seriously considered building my sump out of acrylic. The primary reason for this is I can cut acrylic myself with easily available tools. As stated above, the glass sump will have all the cutting work done elsewhere (that I pay for). The problem is the acrylic sump cost far more money due to the expense of quality acrylic material and it will be more work for me.
For a DIY, it’s much more cost effective to get the glass cut professionally then to buy raw acrylic and cut it yourself. That made the decision easy.
Glass is pretty much forever. Glass will break due to stress. On a tank, this will either be accidental or because a seal/seam has eroded. Even then, the glass may survive (not that it matters once your floor is covered in water).
Acrylic ages and changes composition over time. It tends to yellow under long term UV light exposure. It will warp under constant pressure (yeah, that means water in the tank). It actually absorbs water over time. It simply isn’t a great material for this task.
Acrylic can look exceptionally good on day one, but long term glass is the clear winner.
What do you think about Glass vs Acrylic?
Custom aquariums goes into more details here.