Despite that the provided pictures are small and not of the best quality, to me (and others that posted initially) it looks everything like nutrient burn and nothing like pH problems. And if your pH is around 6.5 like you stated in a previous post then we can be pretty positive it isn't lockout.
I can't say for certain, but I am not sure that a seedling would even exhibit symptoms of lockout if it can still be fed by its cotyledons. Maybe I can do an experiment and intentionally start a seed in a mix with a pH upwards of 7.5 so I can see what happens. I still wont know for about a week though.
And whether it is nutrient burn (which it is)
or pH problems (which it isn't) the solution in either case would be to FLUSH with distilled, filtered or reverse osmosis water that
is the proper pH (about 6.0).
(For future reference:
http://www.icmag.com/ic/showthread.php?t=11688
Or:
https://www.rollitup.org/marijuana-plant-problems/157345-have-plant-problem-check-here.html)