Hey, if you check your dimensions of the tank, and the thickness for each glass sheet, you can check online on a 'glass thickness calculator' to see if the glass thickness will hold the tanks potential water volume. If it cant hold its full the load you should be able to figure out from the chart how much it can hold, generally speaking if it is a 4 ft tank of no more than 18" high 6mm of glass front, 4-6mm side is fine. but do check the calculator. The only other real factors to consider are whether it is made out of weaker laminate glass (test by flicking a normal window/glass and also the tank and comparing the sound) Or, the type of silicone used, the strength is not the issue, it is all strong, just only aquatic grade silicone will not leach toxins into the water. if the tank is strong enough, you can always run a bead or AQ silicone over the existing to prevent issue. 
