I agree, to early for the kim leaf`s to yellow, do you run low RH and water a lot with Tap water ? and do your Tap keep a lot of Ca (calcium) ?
might be a PH issue ? to alkaline soil might lock out the Mg/N even this early, I had one of this with a RH on 30% in a small Cup had to water every day, used Tap as usually, but since the water did evaporate so quickly I added to much Ca in a very short time, top soil looked a bit like yours, had to make a quick repot in to a bigger pot with fresh soil and mist em with PH spring water with a bit of Epsom salt for a few day to turn it around ..