the soil ratio is by volume, and it is just a starting estimate, each person should adjust for their setup and conditions accordingly.
we currently use a decomposed granite soil, it is addressed in our FAQ, right after the first soil FAQ, they are both tied together.
the 50/25/25 mix works well, and you can buy the ingredients at Home Depot. it is NOT the end all to be all, but it does ENOUGH to allow for a decent setup, and most importantly, to LEARN how and what works E:
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robyn@proexotics.com
Pro Exotics Reptiles