1” Horticultural Lava Cinders are naturally formed, pH neutral basaltic stone from northern Arizona that make an ideal growing medium for aquaponics. It is sized from ½” to 1″ and has a deep burgundy color containing a little fines. Like other volcanic rock, lava cinders have lots of pores resulting from expanding gasses when the stones are formed. These pores provide the perfect habitat for beneficial microbes to grow. Cinders are a less expensive alternative to expanded clay or pumice. It is denser and will not float providing a more stable medium for growing plants.