I would limit my numbers to a small school 5-6 fish. Buy them young let them grow up together . After they are adults they will spawn maybe if your tank conditions are to their liking. Look for a fish with a swolen mouth that's not eating cards are mouth brooders. Take that fish out and put it in your qt or hospital tank after a bit it will spit out the babies the fry are fair sized so they can take brine, cyclopees etc. Make sure that they have a varied diet and be ready to do a lot of water changes. I wish you the best of luck cards are among the easiest s.w. fish to breed in tank.
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Max