Scale loss?

[Jessiefish]

Kroenen (who is housed in a 3 gallon Eclipse tank with an African Dwarf Frog and three ghost shrimp -- they've all been getting along great) was fine this morning, but when I got back from a day of fun at the corn maze and pumpkin patch, he had some scales missing from the top of his head. The patch is not white and/or fuzzy. It's not red or raw. He's not scratching himself on everything in the tank. And he's not exhibiting any other weird symptoms or behavior. Is it possible he just banged/rubbed his head on something? I don't have anything sharp in the tank, but there is a divider on the top of the tank frame and I have a couple pots in the tank -- they aren't sharp but could be abrasive if he rubbed up against them really hard.