I believe that is one of those epoxies that specifically say on the back not to use on aquariums. If it's for cars, it's not for your tank. Even if you buy the stuff made for aquariums, you'll still have skimmer troubles. I also feel epoxies don't really work to well in the tank. If you have to use epoxy, buy what is designed for aquariums for the extra couple of bucks. IMO, I wouldn't bother with epoxy.
The JB weld I used in the past are more like a paste, not the putty stuff you would use in the tank for glueing frags or rocks together. Strong stuff but takes a while to set, we used that brand a lot on aircraft.
The putty epoxy stuff are totally different and I can't find any around here that I would use in my tank. I used to buy EP-400 putty at HD out west, pretty much the same color and property as the stuff with "tank safe" label but 1/2 the price.
DO NOT USE JB-WELD..that is for cars and automachanics.i used it to hold my MH fixture in my hood..that is the only aquarium use it has....it contains oil and other harmfull stuff..go with gel..but then again silcone is great stuff