Before contemplation of another species in your tank I HIGHLY HIGHLY recommend that you do extensive research on the ones you currently have. Clearly you have a lot of misconceptions as far as your current stock, and you need to get them taken care of before you add more fish to the puzzle. How long has your tank been setup? Is it fully cycled with good water parameters? Some fish are very sensitive to new tank setups. Do a lot of reading and carefully plan out what you want in the tank, make sure all the fish require the same parameters and get your current stock sorted.