Owing to an accident in which the pot was broken, I am having to repot a 20" Firethorn. It is currently potted in an organic mix but I am thinking of changing to an blend of 1/3 akadama, 1/3 pumice and 1/3 lava. Should I distribute some of the existing organic soil into the mix or strip it away and start more or less fresh. Any advice is welcomed.

I try to get rid of as much of the original soil when I move into bonsai substrate.