tropical fish dying after changing water

Question
Yesterday I did a big tank clean (which I have done before) of my  litre tropical tank which had 5 tiger barb in it.  This morning 2 died and another is on its way.  What could I have done wrong.  I put my normal tap water chemical and cycle in.  I am at a loss.  Do you have any ideas?

Answer
Hi Kay,
 It is important to add the cycle to the water before you add that water to the tank.  Doing it the other way can severely shock the fish.   That said, I recommend that you change no more than 25% of the water at one time, and you should do this once a week, every week.

-- Ron
  rcoleman@cichlidresearch.com
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