From the limited research that I did you would need to have extremely soft water to breed the Cardinals so it has to be rain or even RO water to get it as soft as required.. How soft is the water you are planning to use? Another common issue I found when I looked around at how to do it was sourcing young enough fish, apparently the ovaries harden and the females become unable to lay eggs if they aren't spawned from young, and if they are grown in the wrong conditions they never spawn.
Regarding the breeding for money thing, I only keep and breed species I like that way you actually put the effort into them. I would love to say I cover my costs but I am not sure if I took into account everything that I would, but I do know that I can pay the increase in the power bill and for fishfood and sometimes even cover some new ones so that is awesome After all it is just a hobby but it is always good to cover costs along the way and breed and sell some nice fish meet some nice people..