I have one that does that, I have yet to notice anything that causes it to puff up, mine has been with me almost two years and seems happy and has nice color...try moving yours to the sandbed if it bothers you...the one I have that does that, seemed to puff up more often when it was in my rockwork... I moved it to the sand since I was worried it might puff up too much, fall off the rocks and injure itself...it still puffs up but not as much now that it's in the sand.
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