They are there for protection and bracing. An acrylic tank is usually is euro braced with a solid top unless it's rimless which calls for thicker acrylic. Large glass tanks are built in place most the time all the supports are glass. A glass tank sits on something a little more giving. Although I have abs plastic which I can't make it out of but that tank is 1 inch thick acrylic. No need for it. Sometimes I will tig weld aluminum angle iron around top if it's a wide. Acrylic is more impact resistant and stronger then glass.
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