Grow slow?? im assuming you mean after the get to about 4"-5". Because mine went from 1.5"-2" to about 4.5" in lest the 2 months. but since hasn't gotten past 5" in the 6 weeks since.
my raphael is almost 5 and still really small. i've never seen him eat and he remains halfway out of his hiding spot at all times, perched up rock with java fern growing on it, he loves it and looks dead all day long