Lava rock (scoria)
Also known as: Volcanic rock, Scoria
Preferred
Properties
| Bacterial surface area | 400 m² per m³ |
|---|---|
| pH effect | alkaline at first, washes off |
| Weight class | medium |
| Longevity | indefinite |
| Cost tier | low |
In a system
- Very high bacterial surface area for a natural medium, roughly 350-450 m2/m3, thanks to its vesicular (gas-bubble) porosity
- Around 800-1000 kg/m3 flooded, several times the weight of LECA, so bed framing must be sized for it
- Fresh basaltic scoria slowly releases calcium and magnesium as it weathers and can nudge pH upward during the first few weeks, so cycle the system before adding fish
- Sharp edges can cut hands; wear gloves during installation
- Cheapest option in volcanic regions (Pacific Northwest, Iceland, New Zealand, Italy) where it is sold as garden mulch, but expensive elsewhere because of shipping weight
Notes
Source it from a landscape supplier in 19-25 mm grade, since aquarium-grade lava is the same material at several times the price. Avoid dyed barbecue lava rock, which fragments inconsistently. Lava rock is scoria, a vesicular basalt; its silicate minerals slowly weather and release calcium and magnesium, which is why fresh rock can raise pH a little before the system settles.
See the full aquaponics media reference for comparison, or use the aquaponics system designer to plan a complete setup.