We use and sell lava rock pebbles. This is the same lava rock you are probably accustom to, just in smaller pieces. Lava Rock creates an open airy soil. Lava Rock has a slight mineral content, red more so than black. Rinsing several times elliminates most of it. Excellent in Nepenthes soil and as a soil decoration. It never breaks down and from what I can tell has no effect on ph.
These smaller pieces may be available at home improvement/landscaping facilities in 40 pound + bags. RINSE EXTREMELY WELL, numerous times, with pure water. At the bare minimum rinse until the water stays clear.The lava rock we sell is rinsed and ready to use.
We offer all of the listed carnivorous plant soil parts, and various mixes thereof, by the quart and gallon. Click the "CP Soil" link above to go to the store. You can learn about other carnivorous plant soils by clicking on their names above. Which is highly recommended.