foil is horrible for acid...tin foil (All aluminum) develops condensationw hen there's a change in temeprature...the condensation will destroy the acid or at least get it on the aluminum instead of the paper...put it in a baggie hidden away in a drawer and you should be good...I stored acid for over 6 months and it was good when I took it...I've bought doses that were highly degraded from the same batch because it was kept in foil and in the fridge...you want no moisture and a fridge/freezer will definitley provide you with moisture.