In your stage a foliar feed with Fe would be best and fastest acting.
Second best would be a mineral nutrient that has Fe(Iron). Check the nutes you have if they contain Iron, maybe you have some already..
Ok i get all of that. But what about the flowering? Should I flip to 12/12 or keep it at 18/6? Because either way it still hasn't done nothing in the way of flowering. Also that clone that i took is in a pot of soil rooted and I'm keeping it just to see what happens under a 1212 light cycle. If the close starts to put on real blooms within the next week then I'm switching this plant to 1212 as well.
From the moisture meter it certainly looks like it but hard to say on the calibration/ function of it. The plant is certainly not showing any signs of needing water yet.
Easiest way to tell growing in pots is by weight of the pot.
I would go light on the water when watering and see where it goes.