It is two species of live bacteria suspended in a clay dust, it is a grey powder. I have used it and while I cannot fully credit the product because like most hobbyists I throw everything and the kitchen sink at problems I am trying to solve in my tank but I believe it works as advertised. I am highly skeptical of bacterial products, mainly because I have been in this hobby for 30+ years and the oldest bacterial products were rumored to be nothing but septic tank digester and never worked as advertised. What sold me on this product is we are not the guinea pigs, it was developed by a large French bio lab for use in commercial aquaculture. It is developed to prevent vibrio ulcers on fish and shrimp and clean up sludge from the high population densities. Basically it is a proven product used for many years in aquaculture. One species of bacteria eats sludge and that I can attest to, you will see any accumulated detritus disappear in short order. The other is an enemy of vibrio and attacks it, the hope in aquariums is it would combat RTN but I cannot verify this and that would be hard to do as one cannot say if it was prevented or just never happened, I don't believe it could cure an active infection. I requested a sample back in March as in my new tank I had a strange brown hair algae I have not encountered before, it looked like brown derbasia, one of the promises of this product is that in new tanks which tend to have algae due to an imbalance where algae gets the upper had over normal bacterial digestion of waste, it will bring that into balance. It took 6 weeks and the algae was gone following the recommended 2 weeks of booster dose and 4 weeks of normal dose, the 6th week it literally dissolved and disappeared within a day of the last dose (it is dosed once a week). As I said though I also ran GFO, carbon dosed, water changed, manually scrubbed, added more snails, the usual algae combat we do so I cannot claim any proof it works, all I can say definitively is within a day the detritus is largely gone and the water gets very clear, some of the clarity I attribute to the clay likely acting as a floculating agent, the water turns milky when it is first added.