Very weird growth on seedlings.

I've seen this before. the medium is buggered, roots are getting super saturated and not enough air is exchanged. causes root rot. Next run mix more perlite into the medium blend and try and control your watering habits. Can help it a bit by adding in a bunch of microbes/enzymes to off set the rot but only when it needs more water don't just add it in. It can recover but it will take time and if they autos it will stunt overall growth.

i'm fine with weird growth early on, but if it continues, It's just not worth carying dead weight along with a crop. If leaves are mutated or have a virus, it'll rarely produce properly. This is easier to choose when if oyu are supremely confident about how you fertilize and grow a plant. If yo regularly have to make big adjustments and react to leaf symptoms every grow, it's harder to rule out nute-related issues. If 95% of your plants are relatively awesome, historically speaking, it's easier to blame outside sources. Looks like at least 2 of the others have similar issues, even if not as extreme? Same strain? same batch of substrate? anything else using that substrate that is perfectly fine? would help rule out a virus/pathogen of some sort. i would think there'd be more probliems if it were nute or pH related. These look a bit off as far as lushness and general health outside the obvious issues seen, but not a smorgasborg of leaf symptoms, either, which usually accomanies problesm with nute-lockout or ph balance being off so much it can cause such a drastic effect. you may never get a confident answer here... if you got a backup plan, i'd switch over. Otherwise, let them grow a bit longer and see if they snap out of it.. i think it has genetic and or pathogen issue.

Looks like a soil pathogen of some sort, most probably will be fatal. One plant might be a genetic mutation, but multiple plants indicates a bigger problem. These symptoms are not the result of deficiencies, insects, or pH "swings"............this is a pathogen attacking the plants. Did you re-use any of your soil from previous grows or use the same pots without cleaning them thoroughly?? Plants are way over fed too, btw. Could also be some sort of root attacking nematode? Cutting and pasting is not answering questions on a personal experience level...........anyone can google info.

Am I seeing thrips?

I'd check the ph like Scrubbyjimbob said. The leaf tips curving like that is usually am indication of a ph swing. Just from my past experiences anyway. Best of Luck! Happy Growing!

If it was just a plant or two I'd chalk it up to genetics but if it's affecting half your plants, across different breeders, the the culprit has to be on your end someplace. Root level issues can do weird things to your plants. It could be a pH swing or maybe you should try up potting them.

This is a tricky one... hmm my guess this is overfeed of Mg bs of that block of Ca and P can u tell what % NPK and Cakmag did u feed em with the last 2 weeks ?

Hi bro, Possible Causes Genetic Mutations: Rare but Possible: Sometimes, genetic mutations can occur during seed development. This can lead to unusual growth patterns. Confirmation: Difficult to confirm without extensive genetic testing. Environmental Stress: Heat Stress: High temperatures can severely impact seedling development, leading to distorted growth. Light Stress: Too much or too little light can cause abnormal growth. Nutrient Imbalances: Deficiencies or excesses of certain nutrients (especially nitrogen) can cause strange growth patterns. Overwatering: Soggy soil can suffocate roots, leading to stunted growth and deformities.   Pests and Diseases: Some pests and diseases can cause distorted growth, though this is less likely in seedlings. Hormonal Imbalances: External Factors: Some environmental factors can disrupt plant hormone production.   Internal Factors: Genetic factors or nutrient deficiencies can also affect hormone levels. What to Do Isolate Affected Plants: Separate the affected plants from healthy ones to prevent potential spread of any disease. Review Growing Conditions: Temperature: Monitor temperatures closely. Ensure they are within the ideal range for cannabis seedlings (around 70-80°F or 21-27°C). Light: Adjust lighting if necessary. Ensure seedlings receive adequate, but not excessive, light. Watering: Check soil moisture regularly. Water only when the top inch of soil feels dry. Avoid overwatering. Nutrients: If using fertilizers, ensure you are using the correct amounts and types for seedlings. Observe for Pests and Diseases: Carefully inspect plants for any signs of pests or diseases. Document: Keep detailed records of your growing conditions, including temperature, humidity, watering schedule, and any changes you make. This can help you identify any patterns or correlations. Consult with Other Growers: Discuss your problem with experienced cannabis growers. They may have encountered similar issues or offer valuable insights. Important Note: If the problem persists despite your efforts, consider consulting with a cannabis specialist or a local agricultural extension office for further diagnosis and advice. Good luck buddy.