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The tube didn;t have anything to do with it. Glass is made under stress. It allways has unseen internal stresses and sometimes, even years after manufacture, it can crack with the slightest weight or anything.

You can take a piece if glass and silicone it over the crack. I've done that with great success on the side of my 10g sump when I crack the heck outa it

do you silicone the piece of glass around the edges or all over the piece?

Silicone crack, then around edge making sure no gaps. Then I do a zig zag in the middle. Make sure glass is supported on other side when you press patch on, so you don;t push the cracked piece out. let cure 24 hrs before adding water.

Are those baffles in your sump made of acrylic and your sump made of glass? How tightly did they fit and were they siliconed in? If they are acrylic are they extruded or cast acrylic?

If the baffles are acrylic and tightly fit then it's possible the acrylic swelled as it slowly took on some water causing increased outward pressure leading to an eventual cracking of the glass. Extruded acrylic will take on slightly more water and swell more than cast. Hence the reason baffles should either be made of like materials or not fit too snugly.

damn i think you may be right! i think the acrylic was prett tight. i'm going without baffles this time anyways to lazy to do em again.