Well my opinion shouldnt matter cause your in dirt
but i think they just need 3 days to bounce back
You mention your ph was pretty low
Probably made a slight lockout . Due to the purple on your stems but your mid leaves are green enough
Drooping is proably due to over watering.
I have 0 exp with ff soil or any real soil
But i would just let it be for 3 days and let your medium dry out some
Then give her some plain water at ph of 6.3 but i dont know if this is right for soil
Then monitor. Hopefully the purple on your stems stop .
Then if thats the case. and they still yellow the bottom MORE. Then i would feed.......
But from what little i know about ff soil is its HOT for seedlings . So id definitely proceed with caution as far as feeding it anything.
Till you know for sure its actually hungry and not just locked up
Hope this helps some