I think I'm going to have to make a cut and paste version of this:
- Medium?
- Nutrients in use?
- Nutrient amounts being used (and the manufacturer's recommendations)?
- pH of water and water/nutrient mix you're giving the plants?
You also state a number of days. That's since when? Planting the seed? Starting flower (I can't see that)?
Definitely there's some Ca (Calcium) deficiency happening, but you've also got some decent nutrient burn happening (which indicates over-fertilization).