HELP! Week 4 - Leaves yellowing, brown/purplish spotting on lower leaves

[BobbyLoblaw]

This is my first grow, and I can't seem to get anything right. Please check out my imgur link and let me know what you think! I'm currently alternating feeding with pH balanced watering whenever the medium is dry to my first knuckle, which usually takes about 3 full days (this surprised me because I thought coco would dry out a lot quicker). It seems like the plants are both nute-burned and nitrogen deficient at the same time. I definitely over-fed them the first time I upped their dosage, leading to some nute-burn, but I flushed them until the runoff pH was adequate. I transplanted them into 5 gallon vivosun fabric pots a week ago from their starter containers, and they seem to have started growing again, but the yellowing seems to be getting worse. The lowest leaves on a couple of the plants ended up curling up and seemingly dying. I also have two auto-flowers that decided to flower when they were like 2 inches tall. Really the autos seem to be pretty stunted and sensitive compared to the photos in the grow. I have a pH reader that I keep calibrated, but no PPM meter. I run tap water through a britta filter, bubble for 24 hours, and then add nutes or just pH adjusters when just watering. I'm also battling fungus gnats which seem to be under control for the time being. Any advice is greatly appreciated!

I've pretty much been following the feed schedule from this video: https://www.youtube.com/watch?v=9lpk963vdWc
^Though I have backed off of the nutes since burning them initially. I've been feeding halfway between the week 1 and week 2-4 dose since burning them.

Setup:
Plants: Durban Poison Fem Auto (x2), Cali Bay Dream Fem Auto (x2), Ghost Tang Haze Reg Photo (x3)
Medium: MotherEarth 70/30 Coco/Perl (Pre-Buffered + Washed)
Nutrients: GH Flora Trio (Micro, Grow, Bloom + Cal-Mag)
Water/Feed pH: 5.8-6.1
Runoff pH: 6.1-6.3
Light: SpiderFarmer SF4000 (450W Samsung QB) - Currently ~24" from plants
Temperature: 75-80*F (Daytime) 68-75*F (Nighttime)
RH: 55-65%

 

[RagWeedDWC]

I do not grow in a medium(dirt) so this may be a swag. Are you feeding any calnesium or cal-mag?

 

[BobbyLoblaw]

Thanks for your reply! Yes I've been feeding 2ml of Cal-Mag with each feeding, and the Coco that I'm growing in is pretreated with Cal-Mag.