Hi

great forum, watch the forum a lot,

a question I sometimes hear people say that you always have to make sure that everything about the same grain size

for example: akadama 3-5mm. in combination with 1-2mm zeolite is not don, because you always have to use the same grain size.

what do you think?

I think substrates are not worth the discussion. Everybody has their own opinion and their own recipe.

I see people sifting everything to one size and have healthy trees. I see people growing bonsai in full organic fibres with no visible airspaces and have healthy trees.

It is local climate + care + substrate + species needs that make a healthy tree. You cannot optimize one without knowing the other three.
www.growingbonsai.net/characteristics-of-good-bonsai-substrate/