I haven't noticed any growth from mine. I do agree tough sometimes they are much more active than others. I was hoping to keep them in an unheated tankgot mine from rapps about 6 months ago at about 4". hes probably put on an inch since then. he seems to go through periods when hes really active feeding and gets a big gut, countered by periods where he never leaves his lair behind the filter head for weeks and consequently slims down. not sure, but i think his activity level may be temperature dependent.