About the chart above, the top column, in feet, is the length of the tank.
The column on the left is the depth of the tank.
(disregard the fact that they use feet and millimeteres in the same chart, it's like a formula with fractions and decimals together. sheesh.)
For example, the 36x15x15 tank I was about to build would have required 6mm thick glass for all the sides (and bottom) which translates into a hair less than 1/4 of an inch. I was going to use 1/2 thick glass because it's the same price and it would be tripling the "safety factor"
"safety factor" is the number in paranthesis under the thickness in mm.
The first number is the thickness of the long side, the second # is the thickness for the shorter sides.
The measurements are for an aquarium that rests on a flat surface, so the surface holds the weight of the water- not the glass. Technically you could have a 120G tank with 1/4inch glass on the bottom, but of course it would have to stay wherever you build it permanently. The mere movement of picking it up empty could crack the bottom. 1/2 is usually thick enough for the bottom of any tank to be moved empty and to sit on a strong flat surface.
Most commercial tanks have a safety factor of around 3 point something (3.26 I believe. could be wrong but sounds right)
The hardest part would be getting the glass exactly right- for example, if you want a 36x15x15 35G tank, the actual measurements of the glass would be:
Bottom Pane- 36 inches by 15 inches
Front and Back pane- 36 inches by 15 inches
Side panes- 15 inches by (15- 2t) inches where T is the glass thickness. To put it another way, for 1/2 inch thick glass, the side panes would have to measure 15 by 14, since the side panes rest between the front and back pane.
If getting the glass cut by a professional, they will probably get it right. If doing it yourself, you have to keep in mine the width of the glass blade will "destroy" about 1/8 of an inch of glass at the cut.
I guess since I've gone this far I might as well explain construction.
Materials (assuming the glass is pre-cut)
1-2 tubes of silicone (should have extra on hand, 1 tube is enough for most tanks as long as you aren't human and never make mistakes)
pure acetone or mineral spirits
glass of the proper thickness (5 panes for the tank, plus 1 for the condensation tray if you're going to have an enclosed hood. I'm not going to go into details on the hood since you can figure it out.)
1 roll of tape. Duct, masking, or painting tape will work. Hell, electrical tape will work if you have it on hand.
A flat sturdy and out-of-the way working area.
The first step is to thoroughly clean the glass. Pure acetone will evaporate with no residue. Not cleaning the glass is a recipe for disaster.
The siliconing has to be done relatively fast, before it "skins over". If it becomes sticky, then the bond won't be strong. Also, if the slightest break or bubble is in the line of silicone, it will hurt the bond as well. It's better to use too much than not enough. Excess can be wiped off with a cloth dipped in acetone AFTER the panes are joined. (Make sure the cloth is only damp- wring it out well before wiping anything.)
Then, apply a continuous 1/4 inch bead of silicone to the back and left side (against the edge) of the bottom pane. Apple a 1/4 inch bead on the left side (against the edge) of the back piece.
Carefully place the back pane and side pane on the bottom pane directly on top of the silicone, and with the side pane against the silicone on the back pane. Tape in place well. (Only place tape on the outside- don't want any residue for the fishies.)
Then follow the process for the other two sides, making sure the side panes are "sandwiched" between the front and back pane. Wipe excess silicone from outside the joints.
Let dry for whatever amount of time the directions say.
Then apply silicone against the inside joints, with the silicone tube/dispenser at a 45 degree angle.
\ -------->Moving in this direction so the nozzle of the silicone pushes the silicone in place and spreads it.
Do not wipe excess off in this step- It should be restricted to the inside corners only if you did this right.
Let dry, and Voila! All done. Let sit for a couple days, remove the tape, then fill with water slowly a couple inches at a time and check for leaks. Any leaks, if small, can be repaired with silicone by cutting the existing silicone (inside corner, not the joint silicone) out and replacing.
You can use the rag again to remove excess tape residue, but do not let liquid acetone hit the joints- cappilary action will try to pull it in the gap and dissolve all your work.
BTW, this is how I was going to do it, and how all the online resources I read instructed....
Even so, by doing this you release these forums and me (especially me) from any liability. Build at your own risk.
For more details, simply click the links in my first post, or google it. www.instructables.com
also has some good pictures of tank construction.