His slime coat is probably damaged so I recommend you add in something that renews his slime coat. I recommend you buy Stress Coat. It is a water dechlorinizer and it adds a new layer of slime that will help him counter any possible diseases or injuries. Along with this, do more water changes and use Stress Coat as a dechlorinizer. He's most likely stressed so I recommend you turn off lights for a week and cover the tank with a towel so your fish will be more comfortable. You could also add a bubbler so he can acquire more oxygen. Do not add food, he will most likely not eat anything for a week. Other than that, be patient and wait it out, wish you luck.
I'll pop and buy some stress coat tomorrow and use it in my water change in place of my dechlorinator as you suggest.
EDIT - I just checked my dechlorinator, it says this on the back - "Haloex also contains aloe vera, which helps to reduce stress on your fish, reinforcing the body's protective mucus and improving tissue re-growth after an infection"
Is this the right stuff?
He isn't alone in the tank and they only came out of a 4 day blackout to treat BGA two days ago. They were unfed and in pitch black during that time. Would putting them all back into that for another 7 days be too much for them? Is it really ok to not feed them for 7 days?
On the upside he was having a bit of a swim and a cuddle with 'cat' (a female sterbai cory who he is very fond of. Whilst he isn't back to his hyper self it was good to see him socialising and a bit more active.
You know how they have two sets of fins on the side/underside, one set is the pectoral, not sure what the other is called. I've noticed the other corries tend to rest on the side pair mainly when they are relaxing. He seems to be using the underside pair and keeping the side pair off the ground. Do you think this is further evidence of damage to the spines in him pectoral fins?
Thanks again for your advice