If it has hairline cracks, it isn't tempered. Tempered glass has the surfaces rapidly chilled to cause them to be in a high tension stress, causing the core of the glass to be in compression. Any crack at all and the high tension causes the crack to open up and the core expands suddenly, resulting in a gadzillion small particles of glass. If you are lucky the particles don't completely fall apart, but with water in the tank they would. That combination of high surface tension and high core compression is what gives tempered glass its strength. Before it will fail under a load, the surface has to be stressed above the tempering stress.I hear everyone claiming tempered glass can't have hairline cracks, it can. I would not put too much water in it though if it is inside the house, 125 gallons of water is heavy.