This is what I would do, whether it is the correct way or not I dont know, the reason being is that most of us do not have glass clamps to use especialy for a hex tank.
Get all of the silicon off the sides of the glass where it has split, from the the bottom to the top, use a cutter or razor blade. Once there is no silicon on the glass and it is all cleaned you are ready to go. First of all get some tape that wont stretch when pulled. Sit the tank on a level surface, then what you have to do is use the tape instead of the glass clamps to hold the glass together. When aplying the tape make sure you line up the two pieces of glass properly, also aplying the tape should be done horizontaly to the seem as to give the tape more holding grip, make sure you use a few pieces to be sure the galss wont move.
Now run some tape adjacent to the seem on the inside leaving a gap from the seem of about 10mm, this will ensure that the silicon will not get messy and spread further then where you want it, also when you take the tape off it will leave a nice straight edge of silicon. Now you can silicon the inside, use a silicon gun, also after you aply a thick bead of silicon to the tank use a piece of plastic to even out the silicon by running it from bottom to top, once that is done and there are no air bubbles inside seem leave it to dry, 2 days just to be sure. Now you can do the outside of the tank, be very carefull when taking the tape off b/c you dont want to move the glass too much, if the silicon breaks inside you will have to do it all over again. Once the tape is off the silicon inside the tank should be doing its job and holding the glass in place, now you can do the same as the inside when doing the outside , run tape adjacent to the seem, run a nice thick bead of silicon from top to bottom and leave to dry, again about 2 days should be good.
Always test fill your tank after doing this, and if done proporly you should be fine. If you feel that you wont do a good job take it to a professional.
Goodluck. :clap:
