I ran into a problem with Ball's pickling lime, i put a bunch in my reactor and after several days to a couple of weeks i noticed a horrible cyano outbreak,,,, in troubleshooting the problem i cam across the can i used,, it had be "expired" according to the date for several months, even though it was a brand new unopened can before i used it.. anyway, my Kalkreactor can go quite a while without maintenance so i hadn't noticed that the hydroxide had turned a dark brown sludge color.. i have never had any other hydroxide do this no matter how long i left it in reactor,(remember reactor is air tight). so moral to story is you can use it but watch the expriation date