I think I read in this forum you can use Potassium Alum solution
as pickle and would like to know the concentration to use.
I don't know where Potassium Alum is readily available in the US,
but one product that is readily available is Ph Minus (sodium
bisulfate). It's the same thing as Sparex, but less expensive &
doesn't have the brown scum that sometimes comes with Sparex. In the
US, Ph Minus is available in swimming pool supply, grocery, hardware
& drug stores. It's generally about $1/lb.
It works fine as a pickle & doesn't eat holes in things like
sulfuric & nitric acid can.
As for Ph Minus concentration, I usually use about 1 cup /quart of
water. The concentration isn't that critical. If you put too little
& pickling seems to take too long add a little more.