first off, frontosas are not south or central american. They are african rift lake cichlids.
try checking your pH first. If your pH is alot lower than the stores or what the fish is used to, you're stressing it. Next, make sure the other fish are not bullying it. Frontosas are slow, peaceful fish, if you mixed it with sa or ca it may be scared or stressed from the other fish.
They are also deep water fish to bright lighs may stress it. I had to use a 3' light on my 150 to dim the lights.
Provide a few good caves for it.