Wow! 50 Cardinals! What a sight! Must be beautiful. I have 11 in my 90G planted tank and I love them. How big is your tank?
I guess the first thing you need in breeding cardinals, like any other fish, is .......water! Ok, Im joking! But check out these sites:
http://www.geocities.com/Heartland/Acres/3538/http://www.fishprofiles.com/profiles/characins/cardinal.asp
Hopefully that helps!

miley*