Yes - typo. 6 to 10, not 810.

Still might seem big, but it works for me. I also purchased some 'Safe-t-sorb' which is similar to kitty litter, but sold for absorbing oil in garages or machine shops. This specific brand is reccomended by a popular Bonsai YouTuber. It seems to be holding up pretty well in the damp environment, so I will probably use it for smaller trees, maybe mixed with some finer pumice.

It should be mentioned that it is very useful to have some screen sieves of various sizes to 'classify' (or separate) different sizes of substrate particles, and to sieve out the fine dust, especially when re-using substrate.

Could just lava rock be used ? Instead of crushed brick and do you add anything other then the crushed bricks ?

I don't know how lava rock compares with brick, especially with regard to water retention.

For newly collected trees I use just the brick. They often have native soil still in the roots.
For other trees in developement, sometimes I mix in pumice of a similar size. And if I'm worried about the tree drying out, I might add some sphagnum moss.
Then, I will re-use old substrate from re-potted trees or casualties. I would like to say I sift it, but sometimes I'm in a hurry, and just use whatever I have sitting around in old pots, to fill in a newly potted tree.

in addition to this, I use granular organic fertilizer, added right on top, through the season, which turns to a mush and percolates down into the substrate. Much of this eventually gets flushed out, but in fine, dense roots, it stays, and has to be cleaned out in the next repot.

So I think the use of crushed brick is a sound practice, but I'm not necessarily following all other sound practices (like the fertilizer).