This is the 24" tall 60g tank they sell? Looks like 1/4" glass maybe? Is the top frame compromised/broken in some way? To me it seems like that seam is indeed starting to split open and i would not trust that tank personally, best to get it replaced/refunded.
These days a lot of the mass produced tanks are using thinner tempered glass under the pretense that tempered is stronger than annealed glass. While that may be true, ime the glass will still flex a bit under the water pressure and gradually wears out and stretches the vertical seams, especially if the plastic top frame is worn out, broken somewhere, or just poorly installed. Ive seen this exact issue in two different 72x24x30 tanks with 1/2" tempered glass that leaked after a few years in operation and were cracked in different parts of the top frame.
In your case it might not be exactly that issue, but perhaps the tank was poorly built or the silicone was bad/expired, or a combination of all these things. Whatever the case i would not trust it.
Hey everyone, this past weekend I setup a 60 gallon Marineland ensemble I got at petsmart. The tank, brackets and all silicon looked fine prior to setting it up, but after filling with water on Saturday, I noticed white streaks in the black bracket/silicon joining the front pane of glass to the right pane of glass. They didn’t appear to bubbles and were truly white in color. (See first photo) Since filling on Saturday I have drained the tank to about 70% full while I debated the best course of action. Since Saturday, the white streaks have largely dissipated. (See second photo). I don’t have the foggiest idea of what I am looking at. Is this a sign of a seam failure and/or should I return the tank? 
