Cory Cat Disease Question

Question
Hello, I am noticing a red lesion at the point at which the pectoral fin intersects with the body of a cory cat.  

Tank Details:  
I have upgraded from a 10 gallon tank to a 55 gallon tank 5 days ago.  After allowing the 55 gallon tank to run for 2 days, I transferred my fish from my 10 to my 55.   At the time of adding the water to the 55 gallon, I treated the water with TopFin Water Conditioner to remove cholorine, chloramine, and heavy metals.  Then I added TopFin Bacterial Supplement.  pH is 7.6, Ammonia, Nitrate, and Nitrite are all 0.  While I had the 10 gallon, I would make 10% water changes weekly.  I have not made any changes to the 55 gallon yet.  My tank consists of 3 GloFish Danios, 2 Peppered Cory Cats, and 9 Rummy Nose Tetras.  The Rummy Nose tetras all show a healthy glow of red (I've read that they can act as an indicator to water quality and stress).  Weeks ago, I did replace a Cory Cat, since it died due to similar symptons as I'm experiencing now.   Frankly, I thought I tragically injured and killed the fish while I was cleaning the tank.  I'd appreciate any help that you can offer as I'd prefer to be the best possible caretaker for my fish.
Thanks and regards,
Ed

Answer
Hi Ed
Is the red lesion like an open sore or ulcer?  If so, that sounds like it could be a bacterial infection.  Best bet to treat that, quarantine the fish in a separate tank, and treat with some Maracyn Two or tetracycline.  Keep an eye on the other fish for symptoms, and also keep an eye on the cory for other symptoms that may show up.

Also, are you familiar with tank cycling?  Usually those bacterial supplements don't work.  The only one I've heard positive things about was called BioSpira, it's kept refrigerated, and also rather hard to find because of that.  The stuff on the shelves, you don't know how long it's been on the shelf, and usually the bacteria is already dead in it.

I'm not sure about rummy nose tetras, but I know with a lot of fish ie: neons or red tail sharks, when their colors fade that's usually a sign of stress/poor water quality.  So it would make sense with the rummy noses as well.  

Hope that helps and let me know if you have more questions.

Christy