Hello ZenGrower420, the cause for this deficiency is because of a wrong pH inside the soil. You need to adjust and measure pH because cannabis can not absorb the right amount of nutrients when the pH is not within the right range. You can use a biologic pH min adjuster like the one from Biobizz and a cheap pH measuring tool. They are very cheap and for this small investment you will get a lot of weed in return! Good deal if you ask me, enjoy your grow and stay zen!