I suggest you not recycle coco that comes pre-buffered, with these including Canna, Roots, Royal Gold and other quality coco product lines. I presume the buffering done by the manufacturer is gone after growing a plant.
I presume that coco recycled multiple times becomes more like soil, more organic, if only from fine roots breaking down. Mixing coco and soil, working with something in between, risks more problems.
So, maybe only recycle coco if it was not buffered by the manufacturer. If you do recycle, add enzymes and microbes to break down any residual organics; and maybe only recycle a few times or dilute by mixing in fresh with each grow.