I have never mixed soil and coco together. But at 10-20% I would think you would still treat it as soil. Myself, I have never understodd mixing crap into Coco, you lose all the benifits of Coco when you do. But if it works for you, that is cool.
Yer the coco soil i got has all the bat guano and good organic amendments, i mix some in with my westlands all purpose soil to give the organic life a good start and for base nutrients. I know its probably not advisable but Canna terra soil has coco/coir in but still classed as soil, as yet i have had no problems and better growth so like it, dont like my westlands as much though but is good all the same. I believe they add the coco/coir for drainage in the canna soil, stays too wet for my liking though so like to mix it in with my soil as my best alternative.
So this guys soil is fine isn't it guys, organic, mandalla seeds list it and i like the look of it anyway, maybe some drainage would be my only concern but either way it looks good. Am definatly not going for the pH readings he got and pH down dont do nothing for soil. Lets move on to the other problems now guys, we had long enough talking about soil. Peace