I'd like to add that storing Muriatic Acid in the aluminum box may be a pretty poor choice as the HCL fumes are corrosive. Take a look at Using Muriatic Acid to Safely Lower Your Pool's pH. It has good advice for handling and storing MA. I put the bottle in a bag and close it, put the bag in a 5 gallon bucket with a lid that seals and then I put the bucket in a 20 gallon garbage can with a lid that shuts tight.