I bought one about quarter size from seahorse couple weeks ago. After I aclimated I put it in my tank but my vortech MP20 having too much wave so it kept the horseshoe crab floating on the water all nite. It's legs kept on paddling and flowing up side down like stingray. I was feeling so bad so I turned to powerhead off and let it settle to the sand. But I can't keep my powerhead off so long then I turn it back on so I can go bed with a bad feeling about it.
Early in the morning I check on it so I can't find it no where. I was feeling really bad (thougth it died), but I see no shell or body. I kept searching the whole tank around for days and can't find it. Last week I was staring at my zoas and I see the big piece of sand moving like california earthquake. Then it came up, floating around for long time again until it grab into one of my rock and slowly dig itself under the sand.
Couple days ago I saw him got grabbed by the RBTA, I rescue him by hand feed the RBTA a piece of shrimp. I grab it and move it out. Couple hours later I saw it inside the RBTA again this time I stand there to see what will happen to it and I saw it legs kept on paddling paddling and it got loose and it dig itself into the sand again. I haven' see it since. But I notice every nite when I feed the fish it seem to come out.