I did the tests yesterday when the skimmer was not working. I fixed it a few hours ago so its going full blast now pulling a lot of pale water out.
Unfortunately, I live in a small apartments so I don't have room for extra fish tanks, pumps, and other stuff, so no quarantine.
yes, you are right, I just realized those are his nostrils. So I don't think he hit his head, maybe water or something he ate. These gobies are different, they sift though the sand with their mouth to find bits of food. So a lot goes in there and the sand sort of comes out near the back of the gills.
One though was that something got stuck, but that would not explain both side getting red.
Have one other fish in there, Cleaner Shrimp, Pepermint, sea star, and various snails. All them seem to be doing fine. Nothing new was added. Food is usually frozen Mysis which I rinse in salt water first to get rid of the stuff that its frozen in. The Goby actually likes these more then sifting through the sand so he normally waits for that first then dose the sand thing during the day.
Whatever it is, seems to be tied in with his gills. Can parasites do that and get past the gills that fast? I can try to feed him medicated food since he likes the Mysis, but he didn't each much this morning.