Haven't really had that problem since most of my stuff gets repotted yearly. I have heard recently that charcoal will start to release the toxins it absorbs after a time. When I soak the mix before potting, most of the charcoal sinks to the bottom and I dispose of most of it. I don't think you need very much of it, and it is surpose to loose it's activity after a few months anyway.
So way do I use it at all, creature of habit I guess.
