I bought some photographic paper locally from a guy who was giving up his darkroom and getting rid of all his equipment. He kindly let me have a lot of stuff that he couldn't be bothered to advertise, things like tanks, reels, clips and contrast filters. He also gave me a load of fixer. A 5 litre bottle of Ilford Hypam (which is the fixer I normally use) and a 5 litre bottle of Kodak Unifix, which I had never heard of. A bit of research shows that this is a hardening fixer. I'm still a bit of a novice and I don't really understand the difference. I know that most rapid fixer is non hardening. I assume that hardening fixer makes the negative less likely to damage and I assume the downside is a longer fixing time? What about using a hardening fixer for fixing prints? I would like to make use of this Kodak stuff if possible. I'm assuming that shelf life isn't too much of an issue for fixer if still in concentrate form?