Fish that die soon after being brought into
a new environment have most likely fallen victim to new
tank syndrome. There is not much that can be done
to counteract this effect besides taking the proper precautions
in ensuring that the tank and all items within it are sterile
before any tropical fish are put into it. Even after you have
had the aquarium for a while you will need to fully sterilize
all new items that you intend to place in it. Also ensure
that the temperature inside the tank is appropriate to what
your species of fish requires.
Tropical fish are very sensitive to changes in their environment
and changes obviously occur when you first bring them home
or when you change tanks. It is nearly impossible to match
the exact conditions in your own tank to the conditions that
the fish lived in at the pet store.
A loss of appetite is
the first sign that should be looked for when fish are placed
into a new environment. Other than that, fish that have a
case of new tank syndrome typically will appear very lethargic
and move very little. As long as you are sure it is merely
new tank syndrome and not another infection
or parasite affecting the fish there is no reason to move
the fish to a quarantine tank.