Whats wrong with my flagtailed procilodus (sp?)?

I have had a flagtail for a while, and i think its a really beautiful fish. I recently purchased a second one. The new fish hasn't looked well from day one. Its the smallest fish in the tank but ive seen no signs of bullying, its fins are fine and ive never seen it chased. Ive also watched it eating well, everything from flake to pulling at large pieces of mussel. The problem is that the fish seems to mope around alot, often staying right in the bottom corner of the tank and not moving until feeding time. Its body seems to have taken a funny shape, i have taken a couple of pics (not that clear). Its fin seems to always be down like in the pic and behind the fin the spine looks wrong, its alot different to the other flagtail. It has also developed one cloudy eye. My water parameters are perfect, plenty of filtration and plenty of oxygen. I make regular water changes every other day, im 99% certain its nothing to do with my water conditions as all my other fish are thriving.

Any ideas? Have I purchased a sick fish? I dont want to put any of the other fish at risk, but dont have a facility to remove the fish into another tank.

Steve

I think it works out to around 106 US gallons.
6 Leporinus
1 Lima S N
1 Distochodus Sex
2 Flagtails
1 Aussie Pearl Arowana
1 Wallago
1 Large sailfin plec
1 Pangassius sp?

Plenty of potential for some of the fish to get v.large, but i'm aware of that, most are pretty small at present and in my opinion not over crowded. All of my other fish are very healthy.

It doesn't rain it pours! This might and hopefully will be unrelated but during my water change this evening, the second and healthy flag tail decided to escape. A few flips and jumps on the floor, against the wall and then into the net! Now that has developed some redening (if thats a word) behind the eyes and cloudy eye (both). I'm hoping that it has been caused buy the fall, its a fair old drop to the floor but now i'm worried that its nothing to do with that and that it is coming down with something too. I must emphasis again that the tank really isn't overstocked, not with the size the fish are currently and that the water conditions are fine. None of my other fish are showing any signs of illness or stress.