Bala sharks need BIG tanks
A word to the wise, the bigger your Bala Shark gets, the more he's going to freak out. One of these days he's gonna jump out when you aren't around, or else he'll bust himself up on the glass every time something spooks him. I had 3 balas in a 55 gallon, and had to give them up within a year.
They're gorgeous fish, and highly entertaining, but they were not meant for the average aquarium. I wouldn't recommend any bala shark to a tank smaller than 100 gallons. They're just too large, too spooky, and need company from other balas.
You'll save yourself a lot of heartache if you take them back now and get something more well suited to your tank size and skill level. Balas are hardy, but need more space.
Corydoras, a betta, and hardy tetras would be my recommendation.
OH, another note, unless your catfish is a corydora, he'll be big enough to eat the rest of your fish within 6 months. I lost a fish a night once mine learned they were edible.