Leaf lime green and slow grow

Hey guys , I'm looking to use some Epsom salt in my org soil to try to fix the colors on my leaf right now are lime green on the bottom , is anyone here knows how can I use Epsom salt in my organic soil and how much to put and how many days I'll see the difference ??

epsom salts are for Mag deficiency.

Well I don't know wut to do my plants are almost 3 weeks 4" tall and the bottom leaf r turning yellow and the tip of the leaf is curling upi think I overwater I'm using 600watssMHL 2.5" above my plants temp btw 75-81 humidity 50-55% they told me to use some bloodmeal cuz I have nitrogen deficiency so I put some yesterday but idk how long I should wait to see results if anyone has the same problem please I need some help asap , what is the best thing to do , sorry no pix yet