Bleach

6 month shelf life?!  Did not know that...

That bleach you stored for survival reasons to disinfect water 3 years ago is nigh useless. 

So replace the bleach bottle at least every year.  Or use it up.  I will now try to whiten the shower curtain a little, see what happens.  The old stuff is probably a shadow of its former self, losing 90%+ of it's effectiveness, but a whole bottle will do what a half cup used to.  Diluted in the tub water, of course.