Hard call ! Before we all say replace, consider
Only 16 gallons & the crack is at the very top so very little pressure . . Maybe a big glass patch on the inside with a lot of silicone would do the trick. It's on the side so might not look too bad. It's a hair line crack doesn't pass thru the glass,so still has some strength.
If Mordie is tight on the bucks, I'd say go for it. I have done this in the past & worked just fine . If He has the bucks replace it by all means !