one or the other, i was thinking Mg cause it looked like the older leaves first, but on second look, the whole plant looks kinda pale. Look at my plant in the picture I posted, see how dark green it is? Feed them nitrogen and they'll turn like that. Mine actually may be close to too much nitrogen, cause how dark they are, but they haven't been showing signs of nutrient burn and are still growing fast. We took a break from feeding though.