Homemade frag racks

I wonder if I have figured out why my brand new little fish died in my new 12 gal frag tank?  I made a homemade frag rack out of egg crate (I think that is what you guys call it).  Its that white light cover stuff that has a bunch of squares in it?  I didn't use any sort of glue -- just a few zipties.  Does that egg crate need to be cycled awhile in the tank?  Does it give off some chemicals for awhile?  I put the new frag rack in the tank the same day I bought the fish.  Maybe that was a mistake ...  I haven't put any frags in the tank yet.  Now I've changed about 50% of the water, changed the carbon, the filter floss and will test the water tonite.