Im currently mixing 150L of a coots based soil and id like to add 7L of biochar. My current mix is
20L growstones
15L pumice (would have used more but price was too high until spring)
25L leca clay hydro pellets
60L peat
20L worm castings
10L compost
6 cup neem meal
6 cup kelp flour
6 cup crab...