When you say your tank has been up for 4 weeks, did you do a fish less cycle before that? Where a sufficient population of beneficial bacteria is able to process the ammonia and nitrite, into less toxic nitrate.
It usually takes about 6 weeks to totally cycle a tank from scratch.
EBJDs are a very oversensitive fish, so if your tank has only been up and running 4 weeks, I believe it is not totally cycled, and may not be able to handle the high nitrite being produced yet, which would be very toxic to a new EBJD. Other fish may have slowly adapted, but putting a EBJD in at that stage, of un-cycle could be lethal.
Creating the scratching and erratic swimming.
The toxic nitrite, (and maybe still ammonia) would also create conditions for diseases like ick to easily proliferate in the stressed immune suppressed fish.
Please read the sticky on the nitrogen cycle.
