You want the best for your little star, but it isn't always as easy as it seems. Starfish are saltwater invertebrates who require a lot of care and attention. They're not the best choice of sea creature if you're just starting out with an aquarium, as they have specialist needs.
Preparing Your Tank
Starfish react badly to changes in water quality, so you shouldn't attempt to introduce one to a tank that isn't stable and well established. The salinity of your water should be between 1.022 and 1.025, although it's best to stick closer to the higher end of that spectrum, as any drop below the lower figure could equal an untimely end for your pet. Water temperature should be between 72 and 76 Fahrenheit.
Introducing Your Starfish
Once you have your starfish, it isn't as simple as just plopping him in the water; he will need to be carefully acclimated to his new home. Follow the drip acclimation method. Float your starfish in his sealed plastic bag in your tank for 15 minutes to get him used to the water temperature, then pour the starfish and the water from his bag into a clean bucket or container. Don't expose him to the air, as this could kill him. Run a siphoned drip from your aquarium to the bucket, dripping at two to four drips per second; wait until the water has tripled in volume, then carefully pour the starfish and the water into your aquarium.
Feeding Your Starfish
Learn what your starfish eats, as different species have different feeding habits. Some species will be happy simply to eat algae from the rocks in your aquarium, but others need to consume chunks of fish or shrimp. Your starfish's mouth is on his underside, and you may need to place his food directly below him so he can get it easily. Some starfish will take food directly from you.
General Care and Maintenence
To keep your sea star happy, you should keep him in a tank with a minimum capacity of 100 gallons -- larger is better -- so he has enough space to roam. They like tanks with rocks, coral and a sandy bottom, as this is akin to their natural habitat. Avoid using any copper-based medications in the tank, as they're toxic to starfish. Keep your star healthy by keeping your tank clean; install a good pumping and filtration system and be sure to change around 15 percent of your aquarium's water each week.