This was my post the last time I had issues. I was on here dealing with ammonia issues before and now new problems keep popping up. We were good for a while. Fish.....but I do love them. But here is where we are now especially for those who don't wish to read the older thread.
I currently have 2 goldfish in a 37 gallon tank. (Just bought a 55 to start conditioning) I have a common and a comet. We are using a Tidal 110 filter and ammonia, nitrates and nitrites are at great levels. This was our first time owning goldfish since I was a kid and a long time in general since I owned an aquarium. I know for a while we had ammonia issues as the common (gold) was turning black. He is back to normal and in fact they both act fine. He does have some missing scales but there is no rubbing on anything. He will chase his tankmate from time to time but no real hard contact, in fact, it looks like he is not even touching him. I have a cave and they sleep together in it.
The comet, however, had a vein running down the back of his dorsal fin when we had issues and it formed a bloody spot inside the bottom tip. It had diminished but the vein is visible up and down the length of the dorsal. The anal fin has a little vein but also a small white spot. They have always been the only fish in the tank and we have changed tanks as they have grown fast. Nothing live was ever added and we treated them with Tetra Lifeguard as they were swimming erratically, scratching on the rocks and the common had a head twitch. We got them in February 2020 and this only happened a couple of months ago. The only 'live' thing in the tank was I was giving them frozen brine shrimp once a week (thawed). Once the issues happened I stopped that. But now there there is no scratching, flashing or erratic behavior. My wife is doing water changes every 3 days more or less as the ammonia level demands. We didn't know they would get this big but we keep upgrading our equipment to suit them. The 55 will be running 2 Tidal 110s simultaneously.
But I'm not sure what the comet has going on. I am attempting to add a photo but photographing fish is like herding cats. I have the best photos I could grab now, some which show some veining and the white bump on the anal fin.
Any help would be greatly appreciated.