The main bacteria in the retting process is e-coli which can be cultured in various nutrient broths. These contain N P K but not Ca Mg or Na. Yeasts are also present, which like sugars and phosphorous. With some use of Ca and Mg, but tiny amounts.
coco isn't meant to contain P. What is does contain, is just what they couldn't get rid of. If they could make it stable cellulose and lignin, in an inert manner, they would. I have seen that P will accumulate, which canna rely upon through grow. It leaves quite easily to. Like N, it seems to have little interest in hanging on long term.
I imagine your coco has been buffered with some sort of Calmag. That's all many claim to do. Canna have a wider range of things they buffer with, but N and P are not on the list. All it's really about is getting the K and Na levels in check. As they will dominate.
I could have coco tested as soil, but the result wouldn't be accurate. You need a different extraction chemical. Some chloride. My soil lab can't test compost either. It's not so much won't as can't.
Growing is a hobby that's taught me a lot more than I ever expected to know. Posts like this rely on me choosing the right sources to learn from. I don't always see the full picture so don't like to 'stretch too far' and this post is reaching out of my zone.
I'm happy supplying coco with elevated Ca and Mg for that game of musical chairs. So when the K and Na get up, the Ca and Mg can get seated. I know that K Ca Mg triangle will look different in the substrate as extra K comes from the coco. Enough to do a grow almost. Hence Canna feed having about 60ppm. Not 160ppm. While Ca sits at 100 (if independent testing was accurate)
I do wish I could submerse myself deeper into horticulture, but it's illegal here, so not a long term job prospect.
