A full grown oscar wouldn't be able to turn around properly in a 55 gallon tank. A 55 gallon tank from front to back is only 12.75 inches externally(from frame to frame)... which means about 12 inches internally. An oscar that is full grown will average 14 - 16 inches...
I have seen the effects of keeping a large cichlid in a small tank, and it is one of the most heart wrenching things in the world. Imagine a room you have to stay in all of the time but you can't turn around because your shoulders hit the walls.... how happy and healthy would you be?
I have told this story before, now I feel its needed to tell it again:
A customer brought in the most beautiful jack dempsey I have ever seen. The color was brighter than I'd ever imagined and the fish was full grown at 10 inches. The guy had fed it the best of foods a few times/day and done 100% water changes every day, so his water quality was perfect all the time. The problem: The fish had been raised in a 10 gallon tank. A 10 gallon tank is just over 10 inches wide. (a good comparison to a 14 - 16 inch oscar in a 55 gallon tank) The fish's spine was so kinked, which was a permanent deformation because it didn't have the space to grow, the fish couldn't hold itself upright without the sides of the tank to support it, and it couldn't turn around. When it was put into a 40 gallon tank it couldn't swim, couldn't hold itself upright, and died within a week.
Doing something like that to a fish has to be one of the creulest things in the world.
I'm sorry, but I still can't condone all of those fish in a 90 gallon tank... and with the combination that has been listed, it's simply a matter of time before they rip each other apart.
The sores are caused by a bacterial infection and also a virus. In order for the viral infection to clear up, the bacterial infection must first be cleared up. My suggestion for meds is Fungus Eliminator, but please don't dose the tank with salt while using it. Fungus Eliminator is one of the few meds available that is capable of treating bacterial and fungal together, and this is one of the few safe meds to use for these fish with this condition.
Again, I challenge anyone who thinks this tank is properly stocked... take paper and cut it to the dimensions of each of those fish at adult size, (taking into account their width) hold them all up to the tank and please.... tell me where they would go to get away from each other???? It just isnt possible! This is nothing more than a death trap.