Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
The lava rock I get, from landscape stores, is indeed inert, does not alter any of the aquarium tests I have. It sure needed rinsing though! The dustiest material I have dealt with!
I use the pea sized material in refugium/planted sump/whatever. I grow house plants in it, and pump the aquarium water through it.