I believe they have different ratios of Calcium and Phosphorus. Coco tends to "hang on" to Calcium, but later in the grow it gets saturated and ceases to be as big of an issue, unless you supplement of course. Coco can release Phosphorus I think, so Coco products have less of it. I'm still figuring it out because my mix is a Hybrid. It's part peat, part coco. Sunshine Advanced #4. I do seem to have Calcium/Magnesium issues even with supplementation, but there could be other factors at play. My latest batch, I added Azomite Rock Dust, which has a good percentage of calcium and magnesium, as well as other micros. I'm gonna monitor that. I use RO and I've now been adding about 5ml/gal of Botanicare Calmag Plus. It's better, but not the best. However, my plant in bloom seems to be just fine. I have bigger issues when they are young, up to 4 - 6 weeks. I get the rusty necrotic spotting on some leaves, purple stems, and purplish new growth. I use GH nutes though that claim to be Coco safe, but they also have a coco line. I have advanced on the shelf too though and have contemplated going back to it. I've changed a lot of variables though and hate to keep fucking with it. One reason I did switch though is I don't see much calcium and magnesium in the base nute mix. A lot of the additives contain Magnesium though. I bought their SensiCal, but damn, that has 4% Nitrogen and I'm not real keen on using that in bloom. Botanicare is only 2%.