Will magnesium chloride damage my roof or gutters if I use it to try to melt an ice dam?

I have heard that you can put calcium chloride in nylon stockings and toss them over the gutters to melt ice. I have read in many place NOT to use rock salt. My question is, does it absolutely have to be calcium chloride? We have two kinds of ice melt on hand. One is a mixture of calcium chloride and magnesium chloride and the other does not say what it is. I bought it in Petco and it says it's safer for animal's paws, but it doesn't say what it is. There is ice everywhere this winter and there is no ice melt available to buy anywhere right now. So, can I use the mixture of calcium chloride and magnesium chloride? And yes, I know this means we need more insulation, etc. Usually we don't get ice dams this bad.