Those tiny seedlings roots are fragile, over-watering or under-watering is a common problem because it's hard to know when they need water. That's why I weigh my small containers dry and wet to make sure I know how much water the plant uses. I write both weights on the pot and weigh before I water. I use the triple beams for the best results.
But how come can they show symptoms of "overwatered" since i gave them only 20 ml when i transplanted? Can it be because of their environment in the propagator? I think the humidity in there came close to 90%.
Check ph, and if you can, N in your mix, either via run-off or sampling the mix. Are you using water with high chlorine, calcium, or other solubles in it?
You want to let the roots have a dry period as well as a wet period. Wet to dry gives the plants roots both of the best conditions to be healthy.
No feed besides a little mykos. Tap water with around 225ppm..
City tap? Well tap? Changes in H2O? (aquifers and their mineral contents can change over time, as well)
