The center brace needs to be replaced......At best I'd try to drain the tank down a bit to take any unnecessary pressure of the seams itself....When I say take it down "I'm meaning water level". Probably the easiest way to fix it would be to have a glass brace cut and siliconed into place, but for it to be effective....the tank would need to have the water level lowered till there isn't any stress or bowing of the tank, and the brace siliconed into place an allowed to set up correctly. The other solution would be if you know the manufacturer of the tank, to contact them and see about getting a complete top brace for the tank and replace it that way.
