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