I'm not sure about the cracks that the OP has described. I was curious so I looked at the paper work that came with my tank. The below was taken from that.
"Do not use any product which contains ammonia, ALCOHOL or abrasives such as windex, comet, ajax, or other commercial cleaners when cleaning an acrylic aquarium. Use of such cleaners will cause the acrylic to permanently lose its clarity. A soft cloth and water, or a polish made specifically for acrylic should be used for cleaning."
"Do not expose your acrylic fish tank to paints, varnishes, turpentine, or their fumes. Exposure to these chemicals will cause crazing and loss of clarity."
Maybe what the OP is experiencing is crazing which looks like cracks but are inside the panels.