Originally Posted by CCXGT
On a 10G?
The water is less than 12" deep.
Surely there can't be enough pressure in that to crack the glass.
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The short answer is YES, it can!
If glass has too much pressure at a single point, it can ( and usually does) crack. Consider that the water is approx 7.5 lbs per U.S gallon so you have the weight of the water, the weight of the decorations and the weight of the rest of the tank all being placed on that one point. If the tank isn't level or there is a pinpoint pressure on the bottom under the tank, the pressure cracks the glass. Just ask any tank manufacturer
FYI: I have had empty tanks crack when placed on their side but not on a level surface. A small piece of gravel can take out a side pane of glass this way.