There may be several reasons why its looking pale,illness stresses fish out,has your corys have finrot,this needs to be treated by either moving them all to qt tank and dosing the correct amount for corys with anti finrot/fungus meds,although i found not all corys are keen on meds...or do daily w/c on the qt tank,fresh clean water with soon heal damaged fins.
Paleness in corys could also result from the recent move into a new tank,not enough cover in the tank,ammonia/nitrite poisoning,or being bullied by other fish...
Has you have the fin-rot i would treat this first anyway and see how it goes.
The benefits of having a qt tank,is that i've found meds can affect water stats,and treating a whole tank can lead to mini-spikes.Interpet meds i've found the worse for this...
The barbels look quite short on your pale cory...or is that the pic? - what do they look like to you?
I hope your cory pulls through