3 week old tiny anubis seedling deterioration/ problems for a week please help

Hey I have attached pictures of my seedling anubis femenised growing in canna coco pro
It is under 60w CFL 6500k temps around 22centigrade humidity 50/60 I have q oscillating tower fan have watered twice and only when coco was becoming dry it is in a 18l square pot been using tap water left out for 3 days ph at 5.8 no bugs or fungus but use true cinnamon to make sure
About a week ago I noticed the stem was slightly thin in the middle and the next day had broke but not seperated so I taped and used a straw to help that was fine but since then the leaves are a pale green/yellow and I thought it would have atleast been a little bigger, there are a new set of true leaves pointing up very small and darker green which haven't grew very much either I have no idea if tis is a k defficiency or something else and if I should just start again. the smaller top leaves.looking tiny but a good green so give hope but the stunted growth and yellow leaves/burned tips worry me alot this is my first grow I have read a lot over past few months and have growing elite marijuana book but thats all theory any help would be much appreciated thanks

• but use true cinnamon to make sure​
  
  
  
  

there it is,,,,,,,,,the culprit

How so? Not arguing just I heard this helps with damping off and fungus gnats I only used when I found and killed two small white winged flys I assumed to b gnats, and should I just bin it or can it be fixed

You read so much conflicting info online so any tips appreciated I'm going to try giving it some dark as my schedule was 24/0 under.the CFL's hopefully might just save it and try germing another seed in the meantime

Sometimes you just get a weak plant, I would pop another.

I have a pack of Anubis on its way, everything I have grown from Pyramid seeds has been good to excellent so far.