Amazon puffer has pinkish bottom lip

[The Shady puffer]

One of my amazon puffers got a pinkish bottom lip. It just happened out of nowhere overnight. He has a 300 liter tank, parameters aren't out of the norm, the teeth aren't too long, good filter and lots, lots of plants both aquatic and terrestial. He has 3 tankmates and a lot of different fish (8 panda garra, some corydoras and a single bristlenose pleco). There is a lot water flow as they have a very strong pump plus the filter. All the other puffers are healthy and no such sign is present. Their diet consists of frozen bloodworms, blackworms, white and red mosquito larvae and occasionally daphnia plus pest snails. This puffer eats the best of all of them and is also the biggest. They do glass surf about half of their time is spent on it (the rest they either sleep, chase each other, eat and swim against the current). Did he just hit his mouth too hard on the admittedly sharp-edged root or is a parasite/infection?

[Pufferpunk]

Is it possible it's cut from a snail shell? I'd add Melafix to help with healing.