Ehfilava ia a naturally occuring porous volcanic rock which is ideal for biological filtration where large debris is present such as ponds and highly stocked aquariums this natural product is pre tested for impurities before packaging to ensure that it is free of toxinsr we highly recommend ehfilav for aquariums containing messy fish such as cichlids oscars and goldfish ehfilav is also brilliant when used in pond filtersr ehfilav has a massive surface area for bacteria colonisation ideal f