Magnesium Def? Purpleing of leaves on one plant, browning patches on another

5 Weeks old growing in 50/50 coco perlite mix. growing under 400watt MH in 3 gallon pots in grow tent with good ventilation. Started nutrient regimine way too late at week 3 using the roots organics line. What i suspected was micronutrient and secondary nutrient defs i tryed to remedy with General Organics Biothrive grow which has all the micronutes and CaMG+.everything is organic. After a week of the plants not improving much i decided to leach to medium. After this i fed at 1/2 strength with calmag at full strength and got a slight nutrient burn. What i believe is magnesium def is killing my plants! I have a cheap ph stick reader and it puts ph at around 6.4 range. I dont understand why anything would be locked out. After i did the leach, new growth is looking much better but what can i do about the leaves already dying which in one plants case is going up the whole plant. I have been told to foliar feed with kelp. Is it possible to "leach" the plants leaves of salt build up by soaking them with water before i try to foliar feed next time. Any suggestions on how to tackle this? Should i increase the calcium and magnesium, i am very tempted but do not want to burn plants any more.

View attachment 1984646View attachment 1984647View attachment 1984648View attachment 1984649View attachment 1984652