Hey David you have to remember that this is a natural part of the 
ecosystem you have set up.  I'll try to explain it as simple as I can. 
Some people call it new tank syndrome.  In new tanks the waste and 
excess food break down and the first thing that happens is a rise in 
ammonia levels.  This is normal.  A bacteria then come to life so to 
speak and feed on this ammonia.  This is natural also.  This bacteria is 
what we have come to call NITRITES.  Once these peek another thing 
happens, NITRATES appear and kink of neutralize the NITRITES.  This is 
called the biological filter in your tank.  All fish tanks go through 
this and it is natural.  There is nothing you can do to really stop it, 
and you probably shouldn't.  All healthy tanks marine or fresh water 
have gone through this, and they actually rely on this biological to 
help keep the tank clean.  The only suggestion I would give you is do 
LOTS of water changes, even daily, to minimize the effects on the fish. 
Remember that some fish cannot handle the rises in these levels while 
your tank goes through this and you may lose more fish...Keep the faith, 
and be patient. 
 
 
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