and how do you know its actually Na₂B₄O₇·10H₂O? How much filler did the 3rd party seller add? How much of the filler is toxic or will react in unexpected ways? At least if I bought walmart borax from a brick&mortar walmart, I generally expect it to be all borax. 3rd party reseller? Even that's not guaranteed. If the seller is caught, they'll just disappear and another will fill its place. It is all snake oil salesmen wearing masks and unless you get a lab test on everything you order, you'll get burned one day.