I'm done with Cardinals, I had a school of 60 of them, they all did well for about 6 months, then for no reason they started dying off.
Had them on the best foods, Hikari Micro-pellets, thawed blood worms and brine shrimp, water changes every 2 days.
Might have been old age, not sure, but I am left with about 20 of them.
When they go I am going to re-stock, but this time with captive-bred-born Neon tetras, my cardinals were imports, like MOST are, you can buy captive-bred-born cardinals from Europe, but for around $6 each its not worth it.