I'd like to hear responses to this as well - I've got a bloodfin tetra that is acting strange as well. Staying on the bottom near the corner of my QT, and the scales just above his face seem "roughed up" looking. Did a 50% PWC earlier, testing my water right now.
My initial guesses are: Maybe too much dechlorinator in the fresh
water, and it's robbing the tank of oxygen, and maybe too little current in the tank (one measly little bubble stream used to power a bubble convection filter).
The other 2 in the tank with him seem fine, and the 3 in my main tank are schooling spectacularly. Bought them all from the same school at PetsMart, and inspected all six closely before buying them and taking them home.
Might go get some Stress Coat and Stress Zyme to dose the tank with and see if that helps. Looks like he might have just gotten roughed up somehow and needs some slime and enzymes to help him get comfy. Plus then I can ask out the cute checker girl I befriended the other night ;)
Just did water testing, here's the results:
Ammonia: 0 ppm
Nitrite: 0 ppm
Nitrate: 10 ppm
KH: 5 degrees
GH: 6 degrees
Phosphate: 0.25 ppm
Iron: 0.5 ppm
Copper: 0 ppm
Just dosed with a very small dosage of API Melafix (anti-bacterial) to nip any infections in the bud if that's what this is. All 3 fish are up and about (had to rescue one that freaked out while I was filling my test tubes and wedged himself under the filter), and their gill movements are fast, but that's because I just dosed the Melafix. Going to go get the Stress Coat and Zyme right now.