I have just about the same problem on three outa six plants. coco with pearlite. I feed everyday with 2 liter gift using cana coco A&B. Find it hard to believe it's nitrogen but it's easy enough to find out. Nitrogen will green up a plnt just about overnight so I'm giving it a try. btw, that advice is what I read everywhere so I think it's solid advice.
Nice to get yet another opinion though. Thanks for the help