I've been using wine bladders for Xtol stock solution, and it has worked very well. More than six months with no perceptible problems. As is said above, you need to get all the air out before sealing the solution in the bladder. Because wine degrades with exposure to oxygen, I think the plastic is designed to be an effective oxygen barrier. I have been using "Black Box" containers, so there's also protection from light. It's also pretty good stuff for box wine...