Lubao bag for growing biofilm

[Citycode01]

I noticed a lot of breeders using Lubao bags in the shrimp tanks. I managed to find the guy who selling them on Facebook and purchased few. I very impressed how fast biofilm growing on them and how my shrimp love them. 

Is anyone knows how to make them? I opened one and its smell like bacterial supplement. I think its should be some yeast and some bacterial products but would be nice to know exact recipe.