What the substrate needs to do
Use a clean soil-style substrate for Aphonopelma moderatum that can hold its shape without becoming hard, dusty or permanently waterlogged.
For Aphonopelma moderatum, the substrate in a Rio Grande Gold Tarantula enclosure should support normal movement and retreat building. Heavy decor must not be able to collapse if the spider digs underneath it.
Depth
Rio Grande Gold Tarantulas are terrestrial, so give Aphonopelma moderatum enough substrate for normal digging while also keeping the fall distance from the lid low. A stable ground-level hide should sit securely on or in the substrate.
Match substrate depth to the current size of Aphonopelma moderatum. Small slings and fossorial individuals often use proportionally more depth than a large settled terrestrial adult.
Moisture
For Rio Grande Gold Tarantulas, keep the enclosure mostly dry, with with a water dish; avoid persistently damp substrate. Add water in a controlled area and judge how the enclosure changes over several days instead of trying to keep every centimetre equally wet.
Substrate moisture for Aphonopelma moderatum should work together with ventilation. Persistent condensation, a stale smell or widespread mould usually means the setup is staying too wet.
Compaction and stability
Press the lower substrate layers firmly enough that a retreat or burrow for Aphonopelma moderatum does not collapse immediately. The upper surface can remain looser where appropriate.
For Aphonopelma moderatum, keep rocks, heavy cork and ornaments in a Rio Grande Gold Tarantula enclosure low and secure so excavation cannot undermine them.
When substrate needs replacing
Spot-clean waste and prey remains from the Aphonopelma moderatum enclosure. Normal digging, webbing or rearrangement by the spider is not a reason to replace clean substrate.
For Aphonopelma moderatum, replace all substrate for a Rio Grande Gold Tarantula only when it is fouled, contaminated, persistently mouldy or no longer structurally usable.