hey Shelley,
It was quite a shock when Paul told me about the tank, so as Paul has mentioned tanks with floating bottoms should only be supported by the trims and should never be put on foam in any situation. The result is usually what happened to your tank
This is usually the case with tanks built with the 4 side panels sitting on top of the bottom glass. These shouldnt sit on foam as any pressure on the bottom will push onto glass that doesnt give much before snapping or in your case cracking.
Tanks thats built with the 4 side panels sitting around the bottom glass has a little bit of a flex if theres any pressure pushing up on it as the silicone holding the bottom panel to the 4 sides will flex as the bottom pannel gets pressure.
Hope that makes sense
Cheers,
Eugene