New tank, mysterious brittle star deaths (?)

[Partially Submerged]

I set up a Picotope as an office tank yesterday. I added 3 lbs. of high-quality live rock and a thin layer of Aqua Terra Florida sand. The LR had spent a couple of days in a bucket with the water I used for the first fill. A few hours after setting up, I noticed a whole bunch of small brittle stars crawling in and out the rocks. When I came back to work this morning, I re-arranged the rocks and added some GSP and Xenia frags. I noticed that several brittle stars were lying underneath the rocks, weirdly curled up. I took a few out, put one back in as he was clearly alive (but possibly not well) and flushed the others when I was certain they were gone.

 

Now I'm a little worried what's causing the sudden deaths. Obviously with a new tank, ammonia would be a suspect, but the stars lived happily in the same rock and water for days. The sand is new, but it's inert, and I've used it before (same bag even). It is, of course, plausible that there was some die-off in the rock during transport, even though it was a short commute fully submersed in water. But I am concerned that there is something in the office environment that is poisoning the stars. Cleaning agents used etc. I added some activated carbon, just in case.

 

Sorry - long message before I get to my actual question: Are brittle stars known to have any particular sensitivities that are associated with new tanks beyond the usual ones?

[CronicReefer]

If it was cleaning chemicals or ammonia I imagine you would see it affecting the corals as well. It could have been lack of food that killed them being it's a new tank or possibly shock due to a change in water parameters.