Morphed Axolotl Substrate

[Brrich8814]

I need some help finding a good substrate for our morphed axolotl. I’ve heard that coco fiber can cause bacterial infections and a mix of organic topsoil, organic raised garden bed soil and sand is recommended. However, I’m having a really hard time finding the organic garden bed soil that doesn’t have fertilizer in it. Any ideas of what could be used in place of the organic garden bed soil? I currently have the organic top soil and sand.