Deficiency?

Some plants even from the same pack of seeds are just different, I would not be surprised if the one showing deficiencies has a bigger root ball vs the other two. thus eating up all the food faster. I'm not seeing any measurements of your watering system like PH EC or PPM on your diary?? I see you have not feed them till week 5 of the grow according to the diary, just the happy frog medium. This is a bit late into Veg for its first feeding, normally its week 3 or 4. I'm going to guess this was early signs of needing some CaMg, and you applied it, so problem solved. The damage is already done and can not be reversed but the new growth should not see any more of it as long as you keep up your weekly feedings. Here is the feeding schedule for lotus https://lotusnutrients.com/pages/easy-guide-and-recommended-hydroponic-feeding-schedule Would be good to check it out and see how that fits into your feeding habits. I would advice you get a TDS pen if your mixing dry crystal fertilizers into water for feeding. Best be done by weight vs spoon fulls and should always be verified by a monitoring tool. You could get away with out use of TDS or PH pens if you use RO water and the stuff your using is PH balanced for RO. Weighting it out would be a must vs scoping I feel. Over all your grow is looking good despite this little setback. Keep your girls fed and they will give your great results. Best of Luck and Happy Growing!