That is a sad story.

What kind of soil was it in initially?

This past year I found out that akadama clay tends to suffocate juniper for unknown reasons. I'm going to have to repot my tree now that I know that.

I have a hard time keeping my juniper healthy too. Last year I had more parts dying off than growing. This year it had some new green buds that grew only on one side. Mine really hates wet feet and too much hot sun, but it loves humidity from nearby water sources. Many bonsai growers insist on never using any organic soil material, because it does not let the water drain well enough.

I've used black decorative sand too, but haven't had much luck with it in potted plants. My indoor plants usually end up dead by the end of the year. It helps loosen up garden soil a bit, but I think it starves the plants because it cannot hold any nutrients, and it cooks the roots in the summer.

Next year, I'm going to switch almost exclusively to pumice, since it is white and porous inorganic lightweight volcanic rock.