why are my plants dying please help

I am having problems with plants they are about 2 weeks old and one of them is having serious yellowing problems it started out at the tip of the leaf (lower more old ones) and has progressed since..

at first only one had it but now about 4 have it

also on the sickest one the stem is purple and the middle stem like structure of the sick leaves is also purple

this may or may not be a problem because there are healthy ones that have purple stems too

i dont remember the strain name its purple something

i used 50 ml of fertilizer it is a 24-8-16 mix i used 1/2 tsp per 1 gallon like it said on the bottle with a drop of superthrive

my water ph with no ferts is about 6-6.4 with the ferts it is about the same too

my soil ph is a 7

i am using 2 4' flouros with 2 bulbs in each 6500k 24/0

i was using a 2liter bottle for CO2 but it ran out about a week ago and i havent remade it because i didnt think it really needed it right now but i could be wrong

i honestly dont think i over ferted because i have about 15 plants and only 4 are showing this problem

i hope the pictures are good enough i included a pic of a healthy one with a purple stem

any help would be much appreciated

those are sprouts u shouldnt be using and fert yet just water what soil are u using?

i am using supersoil with perlite probably somewhere around 10-15% perlite

dont use nutes. absolutely do not. you're giving a t-bone steak to a baby

It could be P or K deficiency; do the outside edged of the leaf curl down slightly. I would foliar feed with a balanced fert, like 20-20-20, ans see if the problem corrects itself.

thanks for the help im not gonna add nutes again for awhile or wait do i need to flush?

I'd say give her a good amount of water to get that shit away from her roots unless someone more experienced says otherwise. Don't go too crazy though.

bro, those are small enough to replant in a positive soil environment. just replant it and dont use any nuts/newts. you should be good for about 2 weeks, just ph your water. The leaves wont change color but they will be the first shade leaves to die off, the new plant growth should be fine