Depends on the size of the crack.

I had mended my gold fish bowl with super glue (the small tube bought from Mr DIY). This glue is very thin, and it seeps easily into the crack easily. Apply it on both sides of the glass. No leaking and crack stopped, for my case.

For your flat glass panel aquarium, better rest it on a styrofoam sheet so the bottom pressure of the aquarium is evenly distributed. I might see your aquarium will last a few more years.