Here is my take on this and my primary background is greenhouse growing. What you are looking at is most likely a soluable salt injury. Dill especially during and right after germination are extremely sensitive to salt toxicity particularly from ammonia which is the source of nitrogen in most fertilizer. If you are using fertigation or the potting media had a "starter fertilizer" charge which most do, it likely hasn't leached all the way out. Salt injury doesn't normally kill the plant but it will weaken the root system making it suseptible to root disease. The best way to cure this is to water with water without any fertilizer and water until the seed tray begins to drip out the bottom repeat this several times over the next few days letting them dry out in between. The best way to prevent this is to " water through " meaning keep watering until begins to drip out the bottom you should notice a difference in a week if this was the issue.