Puede que sea una deficiencia de hierro si no me equivoco , pero es super leve . Que tal las dosis con microelementos ? ..saludooos ! Recuerda la T del agua de riego
To me it looks like the beginning of an iron deficiency.
A dose or two of a soluble trace element fertilizer available from any garden store, should fix this quite quickly and boost your plants health at the same time.
Cheers, Organoman.