Things to think about when dropping off the kids at the Pool

Last night I made Tater Salad.I put it in a metal bowl and covered it with foil and tonight the foil has little holes in it.All there are are red taters,mayo,red onion,a little dill pickle juice and a few cchopped dill pickles.Now I have noticed that when I make Veal Parm and cover the metal tray of leftovers with sauce with Foil holes aoppear in the foil.Biedy and I talked about this a week or so ago when I mentioned it and he said the same thing about covering Lasagna with foil.Most likely the acid in the tomato sauce but what could cause it in tater salad?