Only use FOOD GRADE. I order mine from Amazon, but you can find at farm supply stores also. Screenshot below is an example from Amazon. 4 lb would last you a long time, because you're only taking a tablespoon a day. I order 50 lb from Amazon, because I give a lot away to people that are toxic or have arthritis, and I also use it in my yard to kill bugs. if you put a 3-ft swath around the edges of your house, you won't have spiders or roaches. Even though it feels soft like flour, under a microscope the edges look sharp, and it's deadly to bugs (bugs have an exoskeleton, and when they walk through the DE it opens up their exoskeleton, and in a few days they dry out and die).
Anyway, when you start using it, after a few weeks your joints will feel like they haven't felt in years! 😁