Whats wrong with my baby??

In no way am I trying to be a dick but check out or re-post in the sick plants forum. You're post will hit more folks with the knowledge you need.

 

looks like an iron deficiency maybe? im no expert but im pretty sure. someone correct me if im wrong.

 

I know a ton of these look the same but good info none the less. You mentioned that the treatment of the two plants has been close but not identical. I think your answer may lie in that information along w/ the fact that it's in a smaller pot. The container size may have magnified whatever the issue is.

And one more thing. Altering the shape of your pot would only create less room for the roots if both pots stayed stationary. If you move them and smash the side in frequently it could damage the roots. Sorry if this is obvious info but it's worth stating.