fixing my cracked tank ! :L

I suspect is sharizan right, silione alone will not take the pressure.
Better to put another pane of glass over the entire length of the crack and silcone it in.
And unless you have an old pane laying around, it may not be worth the cost on such a small tank.
But just to get experience learning to fix one, has a different type of worth/value.
I like to use 2 panes and sandwich the crack, but that's on much bigger tanks, 1 might work on that small one. (like this)

I used silicone on both sides, insurance is in the extra holding strength .
Besides, once you open a tube of GE1, its pretty much a done deal, you might as well use the tube up.

My tank above is a 120 gal, 6ft long, so if it didn't hold, the collapse would be a serious mess.
Here's the tank, after repair and filled.

Not sure what you mean?
I used quarter inch glass on both outside and inside, and beside silicone on the border of each pane, a bead of silione on the crack itself.