I'm afraid you've got a lot of problems with your tank
Where to start...
Okay; cichlids. There are thousands of species of cichlid, from many parts of the world. Many of them are very aggressive, and many need specific water conditions to do well. African cichlids are amongst the most aggressive. They need to be 'overcrowded', in a large tank (at least 200l/50 US gallons), with hard, alkaline water, or they'll just kill each other and/or become sick.
The parrot cichlid is a hybrid of Central and South American cichlids. They're not so aggressive, and need soft to neutral water to do well. They also need a large tank, as they grow quite big. They're much too peaceful to be kept with Africans.
The iridescent shark is not at all suitable for your tank. These fish can grow to be
eight feet long in the wild. They shouldn't be sold in shops at all, IMO.
Many fish 'diseases' are caused by poor water quality. You have a lot of big, messy fish in a small tank, so the chances are your water is not very good. How long has your tank been set up? Have you tested the water at all? how often do you change the water?
Sorry I can't be more positive. Please don't get any more fish until you've sorted out your current problems. If you don't have test kits of your own yet, buy those instead of another fish. It's essential for every fishkeeper to be able to test for pH, ammonia, nitrite and nitrate.