AsNoriuanswered grow question 3 years ago Nitrogen toxicity ( your overfeed ) caused calcium absorption problems.
Slow down with N, you don't need it anyway.
Give next watering only CalMag with up to EC 0.4 from it . It will stop problems spread, but spots will stay. You will need 2-4 to notice slowing down of problems progression.
Sometimes it is caused by too intense light too.
All the Best !