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