What are the dimensions of the tank that you are trying to build?
As for silicone on the glass, the structural strength comes from the silicone BETWEEN the glass, the joint inside the tank itself is simply for water sealing purposes. Also, you better make sure to use the proper silicone. GE Silicone I and AGA Aquarium Silicone are both commercial grade SEALANTS (and GE Silicone I is NOT FDA approved). That means that they are not strong enough for your needs. You should be using either GE/Momentive RTV100 series (available at Grainger) or GE SCS1200 series silicone. These are both FDA approved and are both industrial strength adhesives.
If you are building a 120g, I promise you that 1/4" glass is not enough. I would use 1/2" with a bottom euro brace at a bare minimum.
As for silicone on the glass, the structural strength comes from the silicone BETWEEN the glass, the joint inside the tank itself is simply for water sealing purposes. Also, you better make sure to use the proper silicone. GE Silicone I and AGA Aquarium Silicone are both commercial grade SEALANTS (and GE Silicone I is NOT FDA approved). That means that they are not strong enough for your needs. You should be using either GE/Momentive RTV100 series (available at Grainger) or GE SCS1200 series silicone. These are both FDA approved and are both industrial strength adhesives.
If you are building a 120g, I promise you that 1/4" glass is not enough. I would use 1/2" with a bottom euro brace at a bare minimum.