Welcome.aboard
Most of the threads here states there is metal material in blasting sand.
I'm not sure if we are talking about the same product, but there is/was a black blasting "sand" sold by that chain that actually consisted of metal slag, a waste product from smelting. Some people loved the stuff and used it for years without complaint; others, like a friend who tried it many years ago, reported an oily film developing on the water surface along with an odd chemical smell.
I don't know if there was some difference between one batch and the next...it is, after all, a waste product and not specifically manufactured for its own sake...or if the people who liked it simply had tanks so disgusting that a film and smell went unnoticed.
I saw his tank first-hand right after he installed the black sand; no way I would ever consider using that stuff. I wonder if our bot will take a break from garden equipment sales and weigh in again?