For the largest aroids with thick, strong roots lava rock may be the appropriate choice for that super chunky substrate mix. Its porosity lends itself to well-draining mixes. Lava rock is also often used as drainage and/or as the sole substrate in terrariums where the plants don’t require a high level of nutrients. Lava rock is also great drainage material for vivariums. Lava rock is a great substrate that has a high surface area making it an ideal filter/drainage material that won't break down quickly. We recommend covering lava rock with a material such as horticultural fabric or synthetic screening to prevent smaller-grained substrate materials from filtering down into it. Lava rock is also an excellent biological filter. The large surface area lends itself to a high volume of beneficial bacteria, Nitrosomonas and Nitrobactercomes, that will convert ammonia into nitrite and nitrite into nitrate respectively. 20-30mm Grade
