the crack could have bean caused by the tank not being on a flat surface. You can get some 1/4" hard foam from the aquarium shop to go under the tank before you fill it. But as for the crack i wouldn't risk fixing it, water is quite heavy and the tank could fail at any time losing all water and fish in one go (and your carpet too!)
meconium
December 2010
Change the tank.
In order to arrest travel of any cracks you have to drill a hole at the end of the crack to prevent it travelling further. You then will have the additional problem ' how to fill the hole '
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Try fixfault.com to fix glassware.