When I first tried cardinals, I had them drop like flies. I got them right off the truck, special order at the lfs. I talked to an old-timer hobbyist who told me to feed them baby brine shrimp, preferably live, but frozen would do.
I tried them again, same lfs, feeding frozen bbs starting the second day, and had no losses.
That was just my experience.
Sent from my nerd device.
"Good judgment is the result of experience, experience is the result of bad judgment." --Mark Twain