Okay, so there's no way that pacu is going to survive. It has the potential to get well over 6 inches--like around 3 feet. So you will want to find it a new home soon. The bala shark as well--18 inches, and they need a group.
Before making any suggestions for other cichlids, you need to determine what you have NOW, since some kinds have special needs, some are incompatible with most other fish as adults, and some can be mannerly members of community forums.
For the rest. The tiger barb is likely going to be a pill to everyone in the tank. They can be managed in large enough groups, but I don't think that's any option for you. That means keeping a bunch of tough fish.
Cories: happiest in groups, will likely be okay with most other fish, since they stay near the bottom and aren't obnoxious, but are armoured against mild aggressions.
Pleco--depending on the species, this fish may eventually outgrow your tank. The common pleco can hit 18 inches pretty quickly.
Clown loach--needs a group. Won't thrive by itself. Again, has the potential to outgrow the tank.
The African butterfly won't outgrow the tank, but will eat small fish, so limits what you can add. What I would do is get rid of the pacu, bala shark, the cichlid and the pleco. I'd get 7 more tiger barbs, 4-5 more cories. Add lots of floating plants for the butterfly. The barbs will add the action missing with the butterfly, the cories will help keep the tank clean, and the butterfly will be a quiet centerpiece.
Sorry, overall, I know this is what you want to hear. What is comes down to is that you need to choose--plan the tank and it's occupants, return what you have and start fresh with a tank that will work, or try to keep the mish-mash you have now, and watch them slowly die due to the poor conditions.