Man

Could some one help with my common pleco (refer to the pictures)? (The white spot on the neck) I guess it is external parasite, but i don't know how to treat it. It's been like this more than 2 days. He's still active in swimming and eating. I also notice some abnormal white thing on the side of the belly. PH 7-7.5; NH3 = 0; NO2 = 0; NO3 = 30; Thanks so much!