After 20 years of buying and supporting seachem I might be Thru Totally. Bought two bottles of Matrix biomedia . Each bottle had 20 to 30 other dense rock pieces NOT PURMICE !!! So little internal if any biologic support internally. I am a Medical Pathologist so I understand micropores and things living and dead VERY well. Sad to say I wll be going back to SERA siporax or eheim efhisubstart two TOP notch GERMAN companies that have NOT disappointed me in the 20 plus years I have used their products. In this Case I truly got LESS than what I paid for! Word of caution.