maybe broken

I picked up this aquarium off marketplace the other day and I didn't know it had this crack. I really do not want to replace the whole pannel as that would be very costly. Would I be able to epoxy or silicone it? The crack does not go to the other side of the glass and its only on the back...

So finally decided to buy a Alex and the trident witch cost me a lot of money, I set everything up and waited a few days to calibrate the trident, but it has been reading my calcium as pretty high since I have gotten it and now a little higher after calibration, my salifert says my calcium is...