What the substrate needs to do
Use a clean soil-style substrate for Aphonopelma seemanni that can hold its shape without becoming hard, dusty or permanently waterlogged.
For Aphonopelma seemanni, the substrate in a Costa Rican Zebra enclosure should support normal movement and retreat building. Heavy decor must not be able to collapse if the spider digs underneath it.
Depth
Costa Rican Zebras are terrestrial, so give Aphonopelma seemanni 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 seemanni. Small slings and fossorial individuals often use proportionally more depth than a large settled terrestrial adult.
Moisture
For Costa Rican Zebras, provide a water dish and a moisture gradient rather than keeping the whole enclosure wet. 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 seemanni 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 seemanni does not collapse immediately. The upper surface can remain looser where appropriate.
For Aphonopelma seemanni, keep rocks, heavy cork and ornaments in a Costa Rican Zebra enclosure low and secure so excavation cannot undermine them.
When substrate needs replacing
Spot-clean waste and prey remains from the Aphonopelma seemanni enclosure. Normal digging, webbing or rearrangement by the spider is not a reason to replace clean substrate.
For Aphonopelma seemanni, replace all substrate for a Costa Rican Zebra only when it is fouled, contaminated, persistently mouldy or no longer structurally usable.