Get a liquid master test kit and test your water. Most pet stores carry them. (Personally I have to drive 2 hours to get one.)
The tank did not have a chance to cycle before you added the fish. There is a sticky to tell you how to cycle a tank. It is located here
In my opinion I would take those fish back. I would see about getting some different fish. Something that would be better for a 10 gallon tank. Get some that stay smaller such as tetras or platys. But be careful if you get platys. Only get males unless you want to try to find a place for LOTS of babies.
Exactly what kind of suckerfish do you have? Does he look like this? If so he is a common pleco and can get up to 16 inches. You definately need to get rid of him!
Get the test kit and test the water. You will probably find out that the levels are too high.
As far as the scale loss, I would also pick up some Melafix. It is an antibacterial medication for fish. The bottle states that it "Rapidly repairs damaged fins, ulcers, and open wounds. Promotes regrowth of damaged tissue and fins."
Until you can get to the store, you need to change at least 10-15% of the water daily. This will help to lower the levels if they are too high. It won't hurt if the levels are fine. But I think it will help your red cap feel better.
Let us know how things turn out.