Hi,
I have a small horseshoe crab and he is the coolest thing in the tank. I imagine he will get big as I understand It can ake many many years to outgrow my tank. I have a 75g with a 5" DSB.. he does burrow and dig, but doesnt disturb my rock (about 60 lbs) It also good to have sand sifting inverts in the tank, so...he is so cool to watch.. Also, he only comes out in the afternoon.. Dunno why though. maybe to swim around. They are not good swimers , he will start out in a run and then take off and swim upside down tossing in the PH's..I sit and watch him find his place where he burrows and sleeps but he wil go for hours just digging then changing his mind.. so, i usually dont see where he goes... I imagine if he died while he was under the sand I would have to scour around looking for him.........He seems pretty hardy!!!! .Oh, and he eats meaty foods.
I say, if you like them, get a small one... you can enjoy it for many many years..
Thanking you kindly, Kim