fixing a broken bottom??

[Pharaoh]

I would definitely go with 3/4. 1/2" would be pushing your luck.

 

[Modest_Man]

i forgot to mention, the tank is similar to Koops big tank, in that it is an odd shape, maybe an S or ~ shape ... so the bottom glass is probably in sections ...

to the person who posed about replacing a bottom pane, how did you get the fram off and back on without damaging it? and how did you remove the pane once the frame was off?
i took apart a 30g, and had to break the side panes just so i could get the front, back, and bottoms apart it was a pain in the butt!!!!

I used a lot of shims and chisels to gently pry the plastic trim off. To put it back on, I just applied silicone and stuck it on. The bottom was already cracked, so I just smashed it and pried the chunks off (after removing as much silicone from the inside as I could). I then removed the old silicone with a wire wheel and laid down my new silicone. I removed 3/4" annealed and put in 1/2" tempered. Gave me a whole new appreciation for how strongly silicone adheres to glass.

For the glass thickness, are you planning on tempered or annealed glass? That will help determine the thickness.