I am planning on using a base of spruce chips, diatomaceous earth chips, and probably peat moss instead of my (now standard) coconut coir but I might keep a bit of coir in the mix for moisture retention.
In addition I will be adding Fe, Mn, and gypsum as @TurkeyCreekTrees shared in this article.
I have access to pH probes at work and can grab free acid mine drainage to water with occasionally if I need more acidic conditions (I’ll dilute as needed). This SHOULD give just about ideal conditions based on the reading I’ve done.
I’m not sure what else other than hollytone could be beneficial. If anyone has suggestions please share, I’ll be happy to learn!