First Grow Ever & w/Coco!

This is week 3 going into week 4. They all popped heads above the ground on the 1st. Happy new years! I didn’t take any pictures of the first few weeks. I was too busy trying to get the GH Micro & Bloom nutrients correct. I’m using the H3ad’s Formula for Coco coir. Mixed with perlite & a few clay rocks at the very bottom especially. This is my first grow & it’s pretty hard trying to diagnose the deficiencies I’ve noticed coming into week 4 as I’m preparing to mainline these babies. I have 7 plants. 1 guy didn’t germinate. Personal bag seeds, great bud tho, So I had saved seeds lol. Any advice or help with the yellowing lower leaves. It’s only happening to the 3 bigger plants. Im thinking it’s a lack of nitrogen or calmag. Which is why I switched to the h3ads formula. It’s just easier to mix a pour. Solution going in is (6ml/Gal Micro & 9ml/Gal Bloom ) & 1 gram of epsom salt Ph 5.8 Ec-1200-1400. My tap water has a ec of 200, I use that. Since coco is extremely empty/inert I wouldn’t use distilled water unless I’m diluting a solution for a lower E.c. I know a little sumthn. But I really need advice from some one who is using a basic nutrition regime. Going into Week 5/ Day 28 Update: My crop is suffering badly from Spider Mites & nothing is morning at all. I’ve sprayed diluted 3% hydrogen peroxide with water. I’ve tried garlic, lemon & water, thyme, lemon grass. Man I need some help. I was thinking about begging for another 4 weeks atleast. If my fan leaves last that long. Any advice would be appreciated. I water every 12 hours until I have a nice amount of runoff. Maybe 200-300 ml give it take depending on the temperature between watering. Oh yea I even gave them some recharge like 4 days ago. I’m guessing that’s why they are perking up a little more