you'll need:
-new razor blades
-acetone
-GE II window/door silicone
-caulk gun
Razor blade off all of the silicone that you can. Use the acetone on an old cloth to help loosen remaining, razoring off as you go.
If glass is hazy, stand tank on end, and allow to soak in vinegar 20-30 mins, razor it clean afterwards.
Allow to dry.
Plan to seal the whole tank in one sitting. New silicone doesn't stick well to old/cured. Be generous on the bead that you put down, you won't be seeing it behind the tank's rims or under the substrate anyway.
Allow to cure 48hrs.
Water test for leakage.