My opinion is that you are dealing with a magnesium deficiency. Try a magnesium product, Botanicare
Sweet, Mag Amped from CES, Flawless Finish from Advanced. And don’t be afraid to apply it, magnesium toxicity is not too likely to occur and you are already deficient.
That peeling at the bottom of the plant is normal.
I would also try keeping the pH a bit higher. I know it goes against the general knowledge that coco needs a 5.8 pH but I personally think a bit higher like 6.0-6.2 may do a bit better. The coco does hold onto nutrients kinda like soil, so that should be taken into account here.
And if I may, did you mix the perlite into your coco, or did you purchase it like that?