I have no idea whats going on. 120 litres is about 30 gallons if I'm not mistaken. If that's correct the tank is extremely over crowded and my guess would be that is part of the problem. Is it a planted tank or fish only? If planted ar you using
CO2?
I'd lower the number af fish and keep the tetra's, white clouds, danio. botia, cory (leapard catfish) and barbs in schools of the same species (cut down the variety of species in each familily). All these fish are schooling fish, the barbs and botia can (will) become agresive toward othe fish. For example: tiger bars with other tiger barbs, black tetra with other black tetras (like you have the neons and cardinals). I'd consider choosing the redtail shark and botia as fish to get rid of since they can be more aggressive. Barbs pick on other fish if not kept in groups of 5 or more of the same species of barb.
The shrimp are most likely going to become tasty snacks. The bristlenose needs hiding places and bogwood/driftwood to keep him/her happy and healthy. The BN also needs plenty of algea and/or other veggies to keep it healthy. Giving him/her a slice of blanched zuccini on the bottom of the tank, a few times a week is a very good thing especially if it's a fish only tank.