hay, i do a water change ever two days too but only 15 liters and fish are growning real fast and they take long as to grow and feed them 3 times a day and feed them shrimp twice a week hope this can help
and the fish are
5 leleupi
8 brichardi
hay feed them a bit of shrimp i feed my 2 males and they are bright bright and real healthy maybe its the green flakes you feed them if its not that i dont kow what it is:-)