1. You should always research the different types of fish you are going to be housing together. Certain fish can be extremely aggressive and cannot be paired with other fish of different temperaments.
2. Always use a new or clean bucket when going through the acclimation or water changing process. A bucket that has been used to hold bleach or other chemicals can be very harmful for the fish in your aquarium.
3. Catfish sometimes require freshwater as juveniles and then as they get old they will need a more brackish environment. Make sure you read up on your catfish to learn what its needs will be when it gets older.