| Well, for starters silicone is not a cheap product to manufacture. It is actually quite expensive, due to it's durability and beacaue it is not permeable to anything we'd care about. The industrial grades of silicone are of poor quality. They're not meant to bind things together and hold them in place. Most industrial silicones are just meant to reduce moisture or air in unwanted areas; and to seam edges together. The tensile streangth of each grade varies, and as well with how flexible it is. The "aquarium" silicone, may very well be the same thing, or it could be of stronger caliber. I've never used it. But I have tried to peel silicone off smaller manufactured tanks and it really is hard to do. But if you take it off someone's home made tank, the industrial silicone can be peeled right off.
This goes without saying that, the surface should always be as clean as can be. Free of dirt, water, oil, anything that would interfere with it bonding to the surface. The cleaner the edge, the stronger the bond.
With this in mind, some have been successful at keeping large aquariums together with industrial silicone. I wouldn't recommend it to anyone over a 200 gal system. (Thats alot of pressure) If you do chose to go with a 'best guess" industrial silicone, make sure it is 100% silicone, does not have any other additives and requires a long time to kick, and eventually set. Like the hobby faster is not better. The longer silicone takes to dry, the stronger it will be.
I work with various silicone products, and...not go on for days I would not advise someone to purchase industrial grade for something they're going to be investing thousands in. It may not be as strong as aquarium silicone, clear silicone may sometimes yellow under water, or it may leach catalyst chemicals used to make the silicone kick faster. There is a reason, it is labled against aquarium use. | 
