i have redtail in my4x2x2 and he was 20 inches and gave him to fish shop.5 months later i bought 7x2x2 and went back to shop and he still had the fish so got him back and is has only grown 2 inches but i recomend feeding once a week.as youngsters they grow quick up until about 15-18 inches and then again that depends on how often u feed him.with a baby redtail i would suggest 3 times a week.
