what type of sand to use?

At one time, I was trying to find the material Star Sound Technologies uses for their steel fill, since it makes common sense that the material is not proprietary. I looked on the McMaster-Carr website and found several polishing/grinding grits, and I suspect this is the material Star Sound uses. However, I could not determine which grit size matched.

So, there's a detective project for someone interested.

In the meantime, I purchased white play sand as recommended by others above. As has been mentioned, be certain to dry the sand before filling your stand. I put mine in a 2"-3" layer in a wheelbarrow and let it dry in the sun.

If someone presents the opinion that there is a sonic difference between silica sand, play sand, cat litter or any other sand when loading audio stands or platforms, then it'll be time for me to leave this insane past time.

That anyone has possibly spent their time making such a comparison is almost beyond comprehension.

Almost.