My Soil Mixture

I live in Indonesia where we have a generally wet climate for 6 to 8 months of the year. My Bonsai Soil:
80% Lava Rock (2-3mm)
10% Coco Coir (Medium to Fine Texture)
10% Organic Fertilizer (Fermented Goat Droppings)

I use this mix for all my Trees and have had great results. Free Draining with minimal water retention in our rainy season. During the 3 to 4 months of dry weather I put moss on my trees to increase the water retention. One main reason I don't use Akadama or Pumice is due to the price ($10 per 1/2 kg excluding shipping).

If anyone in South East Asia has any comments or suggestions please let me know.

It is interesting to know your situation. I hope someone gets to answer this.