I often mix coco into my soil mixes around 20-25%, i cannot say if its any better or worse for doing so, you know, 'cos I am not all sciency and stuff, but I feel it helps to absorb and store liquids and adds a nice fibery feel to the mix..
i would say "no need to bother' but you might want a second opinion on that.
Test it. I never trust coco manufacturers. Hydrate a handful. Put it in a plastic cup with holes in the bottom and check the ec of the runoff. I've had coco that's 900+ppm out of the bag and that's too hot for seeds
Flushing can't harm the coco. During the loading process with the cal/mag the coco gets saturated on a molecular level until it can't hold no more. Everything else can be rinsed off, the coco will still be loaded as water alone can't break the bonds between the coco fibres and the cal/mag, savvy?
In terra preta charcoal can make up 25% of the soil. But I'm adding it as I go, since I have about a 1000L of soil to work with. The 10L bag of Biochar is a drop on a hot plate, but it's a start
