Lava rocks 15 litresLava rock in your pond! Using these washed lava rocks on the pond bed or in the filter encourages bacteria to multiply and significantly increases your pond's ability to self clean. It also helps the sediment on the bed of the pond to break down more quickly. The lava rocks stimulate a steady flow of oxygen rich water, which encourages healthy roots and good growth in your pond plants. The lava chunks are extremely porous thanks to their volcanic