Have you tried Perlite? If you live in a Mediteranean climate? I lived in Cyprus, and usually it never rains between April until September. And bleedin' hot too. I kid you not, friends. If you are driving in the bush or along roads, you never turn on the cooling fan, and you wind up the windows to avoid wind burn. That was before air conditioning in cars. The Troodos mountains though are cool. Skiing there in winter.
I have had a few problems with my soil mixes. I used some kitty litter at the bottom of a pot, and - it set like soft concrete. So I had to remove the Juniper and add a better mix. I use the commercial bonsai mix, mix in some course grit or perlite, And some spags and peat moss. Usually that does the trick here in Armidale micro-climates. I also put in or scatter some charcoal and ash from my friend's fire on the surface. I only use rainwater not our hardish, alkaline tap water.
But I am an organic gal, (no jokes guys, LOL)
I find it works well with my trees. With Seasol the two types, and the occasional DL pellet on the surface. And vermicompost on the surface of the soil. (I remove any worms or critters) A bit of moss, etc. (so long as the birds don't pinch it).
I heard or rather read, you can place the pot in water, over the rim, and let the air bubbles stop, then drain. I haven't done that myself.
Good nite
Pat
Pat