That is from the new growth. Don't stress yourself too much. Stick with your coco and GH flora and follow strict PH ranges and don't over fertilize and you will be ok. Get down the process before you start changing everything up. The nutes are not the problem. What you are doing is. No offense but it's the truth in most things. We are the weak link a lot of times. Coco is suuuuper easy just keep PH between 5.7-5.9 and keep tds around 400 for the size they are now and use CalMag. Water every couple days or as needed. You can tell by lifting the pot when they are thirsty.
it usually takes about 3-4 days to show a burn in most cases, thats new growth that hasn't fully developed I use to think the same exact thing actually my first post ever was about this same thing. In a nut shell you can say the chlorophyll is still doing its thing you'll see over time it will be green and then the new growth after it will have that same light yellow. If anything thats a sign your plant is active!! Happy growing!
I keep p.h 5.8 -5.9 temp 67 -77,plenty of circulation,I am New at coco,so I'm always well in to here constructive criticism N o offence takin,,I am useing calmag, and about 350 ppm
Sounds like you are getting dialed in then! Coco is awesome and can grow amazing plants. I am using coco in my veg garden this year. Excited to see what happens. I'm happy to help in any way.