They are very active, and I believe they do get bigger than an inch.
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All mine are about an inch and a quarter and hadn't grown since I got them (noticeably anyway) about 2 and 1/2 months ago so I thought that was where they maxed out. I did just do some searching and saw 2-3" as max size so I get where you're coming from. I'm gonna keep an eye on mine. Thanks for bringing that to my attention. If they had gotten over an inch and a half I wouldn't leave them in a small tank though just so you know so I'm glad you pointed that out so I can have a plan just in case