sir_isOanswered grow question 4 years ago If I had to guess, nitrogen, potassium, molybdenum are your most likely culprits.
If you can, I'd recommend adding some calmag (more the calcium), some molasses (general elements, but decent potassium, magnesium) and/or something like a little bit of kelp or basalt (something with varied elements, particularly microlements).
But then, based on the info, what I'm saying is practically entirely speculation.