QT - Quarantine tank (should be used to house new fish for 3-4 weeks before the are introduced to the main tank to keep infection or disease out of it
LFS - Local Fish Store
TFK - Tropical Fish Keeping
DT - Display Tank
i am not saying anything bad about any store (particularly one i have not been to) but at the end of the day every store is a business and they have a bottom line to worrie about...
at any rate for salt water it is recomended that one use the drip method as it ensures that the live stock are fully acclimated to the new tank...
take a section of air line tubing long enough to reach a container located lower than the top of your tank (i use a bucket on the floor with a small tank set on top but thats just me)
cut the line in half and insert an adjustable air valve (the twist kind to restrict flow)
put new creature (still in there bag) in the empty vessel with bag open
place end of tube in main tank
start a siphon through air tube and adjust flow to about 1-2 drops per-second
place place the now dripping end into the bag with your new friend
and wait until water volume doubles
dump out half to three quarters of new volume into the vessel and continue to drip into the bag
repeat the doubling and dumping three times
then (this is where you must be careful) if the creature can tolerate air for a moment transfer to tank if not then place bag below water surface and release creature to place in the tank...
keep in mind this is how i do it after reading a ton on line and it appears to be effective and has been for me in the past... when using a QT i would use the same procedure by dripping off the DT and then adding the fish to the QT which i set up with water from the DT any how...