Seedling 2wks old starts yellowing

Allow for a dry back of 40-60% In coco. It gives them oxygen and makes then push to find water. Giving you more growth also helps prevent overfeeding and watering, but that's almost impossible in coco. It very well could be a pest issue, make sure you have no bugs or creepy crawlies in there! Very well could be the amount of ppms or PH. Run 5.8 in coco, 5.8-5.9 and don't worry about PH in runoff your fighting a battle you can't win. But what you should worry about is your runoff ppms. When you water and feed always water until 10-20% runoff. Then check you runoff. If the ppms are more then 2-300ppms MORE then the ppms you gave it then your over feeding and leading to a lockout which can look like a deficiency! If runoff ppms is 200 or more ppms LESS then your putting in then they are deficient and need more feed. Hope this helped, please consider selecting me as the answer so I can be eligbible to enter for a chance to win grower of the months contest! Please and thank you 😊

Its in soil no coco. Plagron lightmix.

Magnesium deficiency developing. Coco is free draining and almost impossible to be too wet. I believe in coco a pH closer to 5.8 is optimal. Checking your run off water pH might reveal some surprises.