If the tank was water tight to begin with than your problem is not the tank but the floor on which the stand sits and / or the stand.
The silicone is NOT designed to be the main structural component of the tank, it is there to take up minor forces exerted by water pressure and provide the sealing between panels of glass.
You could reseal the tank (get some good RTV silicone, clean everything really thoroughly and reassemble the tank; this is easier said than done on most tanks or you could get another tank.
On a large tank expect the entire process to take about 1 week of time in between taking the tank apart, cleaning, drying, reassembling, curing, testing.
The reason this happened is because the bottom panel lies on the flat so it tends to bow under water pressure if not supported properly and uniformly all the way along it's length, the vertical front panel is basically behaving like a piece of glass with the thickness equaling the height of the tank. so the silicone ends up supporting the pressure of the water column; it's not designed or suitable for that.
regardless of the way you decide to go, If you don't want to deal with this again, make sure that the top of the stand is still perfectly flat after a load equal to the mass of the full tank is applied to it. that is particularly difficult if you're dealing with older floors designed under more relaxed deflection standards or if your stand is one of those flimsy (but nice looking) thingies that are so popular nowadays.
Good luck, and, if you need any help housing something while you deal with the issue let me know, I can house a couple of things for a short period.
