Safe soil options

[Loridakay]

Hello! I have some question about soil. I’m currently building a tank with a plant wall hanging above the tank. The goal is to use it as a little bit of extra filtration. Water will be pumped up from the tank down the plant wall back into the tank after filtering through some active carbon.

Now I’m trying to figure out what type of soil I could use in the plant wall. I know I need to avoid heavy metals, really any metals. Could anyone point me in the right direction of a possible safe soil option I could use?

Thanks in advance

 

[Skdecoteau]

What about one of the substrates designed for planted tanks? I've seen them at my local Petco and they look pretty much like soil.