Red Tail Black Shark ? Will need a bigger tank as well. They get way more territorial with age/hormones and need a few caves/wood pile or areas. In long tanks like 55g they can set up main territory at one end. They'll guard that area and hopefully leave other fish alone.
For now ? Give him hiding places at either end.
Rainbow Barb ? Sorry haven't heard that common name. Do you know the Latin/scientific name ?
Are they Rosy Barbs ?
Can you post a pic.
Before adding new fish, I would evaluate current stock for long term needs. Consider rehoming at least the two giant fish ( they will be a foot or more with proper care ). The Loaches like to be in groups. You don't have room for 6 Clown Loaches.
Make your tank a more inviting space. I would plant both ends well. Leave center clear except for plants along the back wall.
Research before you buy new fish. I hate having to rehome fish I've raised and grown attached to, so now I buy fish that can live out their life easily in my size of tank.
You did a great job on the tank it's going to look awesome. Enjoy your fish.
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