I agree its nute/salt burn from nutes either added or in the medium. Also dont let pots dry too much between waterings as this causes salt build up and burnt spots on leaves
That soil is nasty stuff from the back garden and should not have been used with seeds you have bought. Carefully re pot into something decent. The retarded looking one is retarded ,where did you get them?
Yes your overwatering. If you keep doing it the stem base will rot and the sprout die. After germination always let the medium dry a lot more between waterings.
Terrible at spelling/typing aren't you?
The issue you have is nute related ,either the soil or the feed. Flush then only feed about 50% of the current amount or use soil not so hot.
Your nutes are too strong either in veg or early flowering and your losing leaves by burning.
This will affect the final weight as there are much less 'solar panels' when you need them most, in flowering.
Back off the normal feed to half and see how that goes from now on and next grow, nothing...
Its a hard one this, i think the seeds are poor quality or could be over watering. When you water the cubes only wet them 50% not saturate them. The seedlings like the medium to dry a little between watering's after germination. Use scales to roughly judge how to wet them 50% then go by feel. No...
If the tips are burnt/rotted the clones are done and dusted ,fucked.
The original yellowing/necrosis is due to overwatering and high rh or poor quality health of the mother plant.
Clones should be watered about once a day after the the first 2 days.
Have them in a dome for the first 2-3 days...