all sorted guys. have been busy with work so havent had time to come back to let you guys know. Adding some water from my year old 55g tank seemed to do the trick
I lost two zebras about 12 months back due to a Nitrite level of .01. They really are sensitive to bad water quality. Never had the problem since - added an additional external filter - although I admit I am a bit paranoid and check for ammonia and nitrites every other day in the zebra tank.