Difficulty in keeping a Mantis alive!!

[Jayded]

Ok so my LFS gave me a Mantis some time ago and they kept him in a jar, fed him and changed his water after each feed. I took him home and put him in a 5.5 x 5.5 inch cube while his tank was getting ready which was bigger than their jar and he lasted about 4 days before he died. I found him out of under his rock on his back wriggling like a dying cockroach one morning and the next day he was gone.
I did everything they did so I dont get what happened. I had read that they were so hardy!
Anyways today I went in and they offered me another one they had found. I took it and did the same thing again as they had done. This one came with 2 small crabs which they said he would make a meal of eventually.
I did the same again, which is what they did in the LFS, I put him in the cube with sand, small peice of live rock and the water he came in from the LFS. This afternoon, I have found him out from under his rock on his back wriggling... what is wrong!?
I changed his water once I found him like this and Im not sure it will make a difference or that it isnt already too late. I just dont get what Im doing different to the LFS that they dont last very long. I am going to ask the LFS next time they get one in can they just hold it for me until I get the permanent home set and then Ill take it but I am not sure that would make any difference either.

 

[Limbo]

Has the cube you are using ever been used as a hospital for fish. My first thoughts are that something in his temporary home is causing the issue. Maybe the tank, sand or LR?

Also, what is the temp in the cube?

Did the crabs survive?

 

[miztic]

The obvious question is, what are your water parameters? and did you acclimate him at all ?

I can't imagine doing it like that, I'd personally set up a fully cycled tank first and make sure the water is in order before putting any kind of livestock in ..

 

[Jayded]

The cube was bought specifically to keep the last one in when we bought him home. I know the LFS guy that gave him to me and he keeps several in them permanently, but I want to give it a better home than that so I bought it just to use temporarily. So it hasnt been used as a hospital tank or for anything else.
The sand and a small piece of live rock was taken straight out of my larger tank which has fish in it and has been running for over 6 months so it should have been fine and the rock well cured. They gave him to me in a really large bag with alot of water so I was able to use the water he was already in to put him straight into the cube without having to get him used to new water.
I had drained abt 25%ish given him a bit of fresh new seawater which I had bought when I noticed he was out from under his rock and not looking so good.
The crabs are still alive in the same tank even this morning.

 

[Jakaru]

They might be hardy but I treated mine like any other live stock I have. He went into a temp 2.5 gal tank with no filter on it at all and I acclimated him for that. I set up a new tank for him. Mostly new sand with water from my 60 and lr from my 60 and acclimated him once again to the new 20. I didn't really let the tank cycle but had nothing to cause a spike. I caught him out in the open being still and I used a straw (I wasn't about to use my hand) and he flicked it but didn't really move.

The next day I couldn't find him till I noticed him peaking out of the lr at me and he has done fine since. I think he's currently going through a molt because he has closed up all his holes that I used to watch him through and hasn't come out to eat today. (crosses fingers)