fish nostril

Hello, My discus has redness in the nostril area for the past few days. What should I do? Should I quarantine it? Here is my aquarium water test results : Tds : around 150 Nitrate : 10~25 Nitrite : 0.5 Gh : 4~8 Kh: 0 Ph: lower than 6.4 CL : 0 Water system: Reverse osmosis (RO)

Hey Everyone! This is my first post on here and I have a question about one of my Panda Cory's faces. It looks like he has a piece of white sand or something stuck in each of his (what I'm going to call) Nostrils. He seems to be breathing fine and was searching for food as cories do as normal...