I think I am the one that using a lot of charcoal as media, I use charcoal from rice husk, not from wood. 40% of my Adenium media is rice husk charcoal, it is the most common media for adenium and cactus grower in here, the main reason is that they are cheap. $1 we can have almost 100 litres in volume, while pumice lava rock will cost us 10 times more.
So far we don't see any issue with PH / alkaline. The only problem that I experienced, if we use more than 50% of charcoal in the media. When the media is completely dry, the charcoal somehow resist water, when we water the completely dried charcoal media, the water will just pass through from the side of the pot, the media will remain dry, if the charcoal is less than 50%, then it is ok
