A couple of days ago I lost one of my goldfish to a internal infection. For that past couple fo days my other red cap goldfish hasn't been eating the food I give them. He'll swim around the food and one in a while suck up a flake and then spit it out. I tried giving them brine shrimp, but he wouldn't eat that either. I checked his mouth to see if he had a rock stuck in his mouth, but there wasn't anything in there. I did a 50% water change yesterday in order to get rid of all the toxins that might be in the water because of the other fish, and I also noticed that my nitrates were at 38. Any ideas as to why this fish isn't eating, he swims around and is showing normal behavior other than the not eating.