Help, Cardinals dying

[chek]

My cardinals are dying, so far 1 a day for the last 4 days. They will loose their red colour on the belly and float to the top of the tank for air, swimming at a 45 degree angle. They will die after 1-2 days. Other than that, I did not notice any other symptons. These cardinals are my first batch of fish load in my tank and they have grown to a nice size. I have green tetras, rummy nose etc in the tank as well and they look unaffected. any idea what this is. Have searched thru many websites (incl this) and I can't find a sympton clsoe to what I described.

[stormhawk]

It can be a number of factors. Are you running CO2 in that tank? Lack of oxygen might have prompted your fish to go to the surface.

It could also be an internal disease, or just stress. From memory, larger cardinals do not adapt to life in a tank as well as young specimens do.