Without your sharing actual numbers, and the fact that the tank is relatively new, I am going to go with transient ammonia burns, per http://weloveteaching.com/puregold/d...#BLACK%20SPOTS.
It takes filters typically 6 weeks or more to completely cycle, converting all ammonia to nitrites and nitrites to nitrates. The first thing you will find is the fish give off ammonia and it will build up until the filter has developed enough good bacteria to convert all that is being produced to nitrite as fast as it is being produced. The nitrite will build up until the filter developes enough of the other good bacteria to convert all of the nitrite to nitrate. Nitrates will build up between water changes and the water changes will reduce the nitrate level by the same percentage as the percent of water changed.
Ammonia burns skin and gills, so the use of a water treatment like Prime, Safe, or Cloram-X is needed to bind the ammonia in a non-toxic form. There is an Ammonia Alert Card by SeaChem that will tell you if it is toxic or non-toxic as the test strips will show ammonia whether toxic or non-toxic. As the ammonia starts to be converted as stated above nitrites will show up and they are toxic, in that the nitrite will attach to red blood cells converting them to non-oxygen carrying brown blood cells. The use of salt at one pound per hundred gallons will protect the fish from nitrites.
Zone 7 A/B
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