do you have a deep sand bed I have a seabee that desided it wanted to be a sand sifting seabee and started crousing around the sand bed and when it felt like it it would hide under the sand. I know they shrink when they have to poop theres just no outher way for them to do it. My pink tip Nem folds it self in side when he does his poop thing and he gets realy small about the size of a golf ball maybe a bit bigger but not much. when exstened he's about the size of a soft ball or a tad larger 5-6" turn the lights on and he will exspand in no time and show him self. Aclimation time may have been a bit short for your Nem and he is just sitting it out till he is happy. There could be a number of things that will make a new Nem do strange things. My pink tip has resently moved him self into a piece of branching coral LR from the rock that he has been on for the last 6 months. It's a new tank to him and he now likes being tangled in this new rock His tenticals have gone green with pink tips very nice colors for him to be. He started out white with pink tips turned brownish with pink tips and now he is green with tip tips. I love how they adapt to thier seroundings and change over time.

Bill