Never heard of 'tube' sand. If there are any quarries in your area, that's a good place to look. Check under "sand" and "sandblasting" in your local yellow pages. Contact some places, you're looking for a #2 mesh.
The mesh number indicates the size. Quarries separate sand by sizes by sifting if through a series of meshes. #2 is about a 3mm diameter to each grain and works great. #3 isn't that much bigger, it is a little, but you'd be hard pressed to tell the difference. Play sand is, I think a #0 size mesh, you can get sand as fine as #00, but that's filter motor killing fun.
The mesh number indicates the size. Quarries separate sand by sizes by sifting if through a series of meshes. #2 is about a 3mm diameter to each grain and works great. #3 isn't that much bigger, it is a little, but you'd be hard pressed to tell the difference. Play sand is, I think a #0 size mesh, you can get sand as fine as #00, but that's filter motor killing fun.