Join Date: Feb 2014
Location: NY; LETS GO METS
Sounds like a recipe for disaster!
First off; the trim on the bottom of the tank is extremely vital to the tank's structural integrity (well on most tanks anyway. You didnt' post a full tank shot; but I'll go ahead and assume that its just as vital on yours). I would't worry so much about losing a little silicone with the trim/brace but would be more worried about the trim/brace itself. Slapping some silicone on the outside does nothing but make a mess. Its not going to help seal a potential leak.
Second, the number one thing to avoid when trying to level a tank is torsion and/or twisting. So its kind of ok if the front is a bit lower than the back so long as the sides are on the same "downward" angle and vice versa. You dont want the front left corner to be a lot higher than the rear right corner as this causes a twist and can potentially lead to failure. Your photos dont really show whats going on; but from your description it sounds like you are experiencing that type of twisting/torsion.....which is very bad especially when you couple that fact with the lack of a bottom brace.
I wouldn't worry about a crack so much as an all out tank failure!
However, the photos you took of the bubble level show something that is very very close to level, but again there really aren't enough photos to tell the whole story. But, what your describing is a bit troubling!
Curator of an ever growing fishroom that currently houses 30 different tanks. Most full of at least water....some even have fish!