It can depend on the tree you wish to keep & the climate you live in.
It sounds like you have lots of organic material in the mix, much of it fine, which means it will retain lots of moisture. That's not a good thing for most bonsai, unless you live in a very dry climate. Even still, you would need to make sure it is thoroughly watered each time, as the surface may appear damp, but portions unseen can still be dry.
Fine particles are not ideal for your bonsai mix, as they clog drainage holes and can retain more moisture than is healthy. Organic material breaks down over time, turning into finer particles. It becomes almost like mud if there's too much of it, which chokes roots & leads to rot.
You'd be better off to add more sifted coarse-size inorganic material, like the lava pebbles you already have. Other available products out there work great, too. Unscented kitty litter (kitty-dama), fired clay soil conditioner (Turface is a well-known brand), chicken grit, gravel, river stones. As long as it's sifted to a reasonable size and not too large or small. My mixtures are sifted to a size between ~2mm-6mm.