Once you get your new pets home it is critical that
you take time introducing them to their new homes. Saltwater fish, and
especially invertebrates like corals, are intolerant of even the smallest
changes in their environment. This includes:
Temperature
Specific gravity
Water quality (Nitrates,
Nitrites, Phosphates, and more)
Light intensity
(some corals are more sensitive to this than others)
If you shock your new inhabitants by changing any one of these things
too quickly, they could die. Most pet stores will give you credit the
first time this happens (some make you provide a water sample from your
tank). But, these are beautiful and rare animals, so take these steps
to avoid any issues:
Take your time. Many new
reef tank pets meet their demise because their new owners are so excited
to see them in their tank. Introducing new species to your tank takes
time (sometimes many hours). Don't rush, and you will be rewarded with
a happy pet that lasts for years.
Acclimate slowly. Your fish
or coral has survived in a bag for some time. Now, you need to change
that environment for that of your tank. By adding small amounts of water
from your tank (a cup is enough) every 30 minutes or so for several
hours, the water in the bag will become the water from your tank. If
you do all of this with the bag floating (use clips, so it doesn't fall
over) the temperature of the bag will slowly reach the temperature of
your tank.
Drs Foster and Smith have a useful video on the subject for more information: