Yep i think this threads your answer, bad pH from high nutes.
Damn bro that seedling looks good so heres where you can find out the results from this thread, give her less nutes over the course of the next 22 days, if she looks better than the 22 day old pics we got a winner and dont forget to post pics, these threads get read for years and nice to show a conclusion right or wrong. Personally dont flush the 22 day old one just go straight water and get good runoff, flushes are a nightmare and last ditch effort, think you will make it through with plain water and keeps things easy and slow.
Thanks for a great thread, i got a lot out of it, others who contributed should also comment. Peace