I can't believe you were sold ONE bala shark.
Sharks... this is for ALL freshwater sharks, require salt. They are considered brackish fish. In the wild, these fish will migrate to the ocean once they are adults.
Add salt. Add the required amount plus a cup of salt to sit at the bottom. Refil that cup once it gets close to empty
Fish will outgrow their tanks. Its pure myth that fish will grow to their tank size. All that happens is the fish dies at a very young age. Fish live for years. Bala sharks, and other freshwater sharks, get huge. The tank you have now is fine, but you plan on keeping them, you're going to have to upgrade to a bigger tank. You are also going to have to get more. Bala sharks, tri color sharks... they are schooling fish. They do better in groups.
Please research your fish before you buy them.
Aquarium Fish: Tropical Freshwater Fish and Saltwater Fish for Home Aquariums
And quite honestly, the person you're going to for help sounds like a moron.. he sold you feeders to cycle the tank then 1 bala shark... ugh..
I wish you luck