red sore = dead fish
 

I always q tine my fish with about 50/50 success with pet shop fish. The ones that don't make it seem to always have similar symptoms before they die. They are good for 2-3 days then develop a red looking sore on their side. Then 2 days later they die. I usually use sea cure for ich and use api medicines for fin rot and for this red sore. I'm just wondering if anyone has some insight to this as I usually pick out fish, hold them for about a week at the store make sure they eat, and are good looking fish. I've lost a powder brown tang, potters angel, and the last one was a nice copperband butterfly. Any help is appreciated

Have you been able to successfully treat anything that exhibits this sore? Do yourfish exhibit any loss of appetite?
Are these fish also experiencing fin rot?
Can you post water parameters?

the fish that I'm writing about are new purchase fish not ones already in my tank, no I have not been able to treat the red sore successfully, no the fish dont exhibit fin rot but I have had success with api meds for fin rot on other fish, the fish seem healthy and eating when I get them but just hang out by the filter intake sponge with lights on, as far as water quality I'd have to check it, I drain water from my reef tank and use that for the qt tank

That stinks.
Water parameters when you get the chance.
A picture would even be great.
I would look into the worst case scenarios first and try to rule them out. Maybe Google Wasting Disease or Fish TB. Might do a little good to clean out the QT thoroughly after finishing with the fish you currently have in there.
I am assuming that you do not have a QT full of fish and that it is probably not an injury from another tank mate or injury from being netted.