Expanded shale
Also known as: Haydite, Permatil, Expanded slate
Preferred
Properties
| Bacterial surface area | 200 m² per m³ |
|---|---|
| pH effect | neutral |
| Weight class | medium |
| Longevity | indefinite |
| Cost tier | moderate |
In a system
- Made by firing shale (or slate) in a rotary kiln at roughly 1,100-1,200 C until it expands into a porous, hard, neutral-pH aggregate, similar to LECA but denser
- Around 600-700 kg/m3 flooded, sitting between LECA and lava rock for weight
- Irregular angular shape packs tighter than rounded LECA, so a given bed holds slightly less water by void fraction
- Does not float, so beds can be filled and flooded immediately without a saturation step
- Commonly sold as a soil amendment in heavy-clay regions (US Southeast); a 25 kg bag costs much less than aquaponics-branded LECA
Notes
Rinse before use. The Permatil brand from Carolina Stalite is the most common North American source, while comparable Spanish and Australian products are sold as 'expanded slate' or 'haydite'. Like other expanded mineral aggregates it is a porous, kiln-fired lightweight rock, here denser and more angular than expanded clay.
See the full aquaponics media reference for comparison, or use the aquaponics system designer to plan a complete setup.