I have one that is missing scales just as yours. He had a couple missing when I got him and it just progressed. But then again, this is the fish that is very suicidal and I've had to literally rescue him many times from getting stuck in/under rocks, substrate, cups, plants, etc. He is not in a bare bottom, very minimal tank because he just can't seem to stay out of trouble.
Missing scales not a whole lot you can do other then keep the water clean (keep up on your regular water changes, you may want to add in a small one each week to keep it super clean. Stress Coat and tannins are great. You can either use Stress Coat as your main water conditioner, or add in a few drops along with your regular conditioner. Make sure there isn't anything rough in there that could of caused it. It may of been a one time accident of being overly curious and got stuck trying to get to something on the bottom, but it's better to check just in case.
Usually they grow back.. unsure how long it takes though =(
The coloring and locations vary fish by fish.. but it really sounds like it's missing scales. Keep an eye on them and see if it gets bigger, or changes color.
Last edited by Myates; 10-12-2011 at 10:40 AM.