it should have hit six inches the first year you bought it, your tank is way way too small. if you put him in a 75 with a powerhead on a timer he would probably be 8 inches. why have you gotten sick of the most amazing fish out there? there incredible. my all time favorite fish. if i were you i would buy him a 75 with a koralia 4 powerhead. that would be the right thing to do.