I filled the tank up with water and it barely leaked out of the crack. But the crack is near one of the walls. I am resealing all the seams, but the crack I'm not so sure about. Shierkahn, I really don't have a piece of glass that big, or the money to buy one, or anyone to help me. Couldnt't I just Silicone a piece of glass onto the inside of the tank? It is going to be covered with gravel. I'm not going to be putting lots of heavy things in there, besides the water and the gravel (40lbs of gravel) and the 400 lbs of water, but thats the thing; the 440+lbs on top of it I think would be enough to break it.