I dont think calling fellow growers 'stupid' based on their tried and tested methods is necessary do you? A seed carries enough nutes of its own to take it to 14days roughly! So imo a weak 400ppm could be given from day 15.id say 3-4 weeks b4 using nutes. thats just me thou. other ppl use nutes at 1-2 weeks but i think there stupid.
it could be heat stress on ur little seedlings that ur refering to