Tell us about your mix.
That's alot of compost. Coco is already high in na and most cow compost is as well. Calcium with balanced p is job #1. What sources do you have of each?Explosive - ordered some chelated iron just in case
Jackspratt60 - 5 gallons coco, 2 gallons cow manure compost, heavy sprinkling of perlite, and 3 tablespoons per gallon vegan mix by down to earth.
I agree, new growth is often pale especially if it is growing fast. Possibly nothing to worry about at all.It doesn't usually happen this early, but a plant's newest growth is often a mountain dew color- neon green/yellow like that. Usually that happens in veg when a plant hits its stride and explodes, growing significantly overnight, and it is young tissue that hasn't fully developed under light yet.
If your lights are dim or too far away sometimes this neon new growth can take a while to turn to the usual dark green. My first guess would just be to move the lights 10-20% closer, and your soil is actually fine.
A couple of possibilities. When the pH of a growing media rises above 7 the plant's tops will turn yellow. The reason is micronutrients need an acidic pH to break down the nutrients into a soluble range.
Another possibility is that the pH is too low causing nutrients to slightly toxicate the growing media causing the plants to yellow. You need to do a pour-thru on a watering day and catch some of the runoff and test the ppm and pH. If your pH is in a good range then the EC is off. Good luck and keep us posted.