It takes years for them to out grow a 30g tank. i have 2 and they are about maybe 2'' long now and have even been moved to salt water for the last 6months because i want them to see that magical 6'' mark. Several people have had them at 6'' but most buy them big. No one really has documented there growth rate but for mine it has been maybe 1/4'' a year. And they are eating shrimp,blood worms, mysis shrimp,snails, so diet is not the problem.