Athosanswered grow question 6 years ago For growing in soil, checking ph and EC/PPM is dead useful, but optional, you can do without it and get good results. For growing in coco, checking and adjusting pH and measuring EC/PPM is a must. Those pictures look like you had a burn, due to overfeeding. Calcium deficiencies show on the newer leaves, not the old / lower ones, so it's not that (and it takes weeks to show) and it looks like red spots on the leaf, magnesium deficiency look like yellowing between the veins of the leafs. pH for coco should be in the range of 5.5 to 6.5, ideally you want to be at 5.8