First Green Crack and first in coco

Hey, it looks more inline with a potassium deficiency. I had a look through your diary and noticed you mentioned you were not watering until runoff. This could have caused a buildup of excess nutrients/salts. Causing the PH to fluctuate. I'd recommend flushing with plain PH'd water. You'll need to water 3x the pot volume (e.g a 10L pot will need 30L of water) this ensures the medium is cleaned out properly. Then you can apply your feed. You cant overwater this way, dont worry. Overwatering occurs when you water too frequently. It is not based on the volume as that drains away. I see you are using RO water. I would recommend getting a cal mag product. As plants need that extra supplementation when on RO water (tap water usually contains this.) I see that yoire using Advanced nutrients, like me. I can recommend Advanced nutrients sensi Cal mag extra. It has an N P K ratios of 4-0-0 so be sure to cut some nitrogen out of your usual feed. Hope this helps 🙂