Valentini Puffer mouth fungis

[paulpad]

My valentine puffer has a purple fungus like stuff growing on his teeth. I asked the pet shop but no luck. My puffer has always been a lazy eater and doesn't seem to chew on anything. This fungus or algae has been growing on his beak for a while and has gotten worse. Didn't bother his eating but lately it has. He has a hard time grabbing the food and looks like he's loosing weight. I've included a picture but not too easy to see. any ideas?