Ok. As a general rule, stars are sensitive to changes in water quality. As a result, you will want to take some precautions to keep them healthy. These probably sound worse than they really are in terms of difficulty, so don't be intimidated. First, you need to be 100% sure that your new tank is 100% cycled before adding anything, but especially sensitive inverts. When introducing starfish, it would be advisable to
acclimate them to your tank using the
drip method. This will ensure that they are gradually acclimated to the inevitable differences between your water and the fish store's water so that they do not die from "system shock" from a sudden immersion in different tank water. Once homed in your tank, some things you can do to be sure they stay healthy: run a protein
skimmer on your tank. In conjunction with live rock, this will help keep your water as clean as possible. Get on a regular maintenance routine, which would consist of regularly (weekly) monitoring your tank's water parameters for
ammonia,
nitrite,
nitrate, and
pH, as well as routinely changing out a portion of the water in the tank. Don't stress the testing, it is simple with a liquid
test kit that can be purchased locally or online. Also, do some research on different types of starfish before deciding which variety to buy. As with fish, some are more hardy than others, and you would be well advised to start with easy care specimens to maximize your chances of success.