Honestly, the tank in post #1 looks to my eye to be completely safe for use. The silicone between the glass panes is what holds the tank together and provides structural strength. It's usually a continuous seal that maintains the waterproof integrity of the tank as well; the extra little concave bead that, in this pic, shows a bit of a ragged edge, is there just as an added insurance against leaks. If this tank doesn't leak now, I doubt it will at any point in the foreseeable future if properly set up on a flat, level stand.
N
nataniah
, sorry to say but the spot where your old silicone meets the new is a problem. However, it looks as though you scraped off the old silicone from the upper half of the corner and then re-sealed? Definitely the wrong way to do it, but it's done now so why not try it out? Any leaks will likely be visible within a day or two.
Whenever you apply silicone, you really have one good chance to make it smooth and neat, right when it is first applied. If you keep poking and squeezing and fiddling on the bead, trying to get it right...which is what it looks like you did...it just gets uglier and uglier. Same if you wait more than a minute or so to "tool" or work the surface. Lay it down, wet your finger and swipe across it once. Practice makes perfect.