Just for the sake of saying it, are you 100% sure its a crack? Even if you are sure get yourself a razorblade or something with a sharp edge and just try to scrape it off. Sometimes silicone looks like a crack. I freaked out a few weeks ago when I cound a crack that looks just like that one on my 105G. Well long story short it scraped right off the glass. Fingernail won't get it, use a sharp blade.
Here's to swimmin with bowlegged women.
Reef with 30G Sump/Fuge Combo
-30G LTAnemonarium with mated porcelain crabs, 10 sexy shrimp, and 2 pink skunks all tied into the other 135G in my system.