If it was gill flukes, you would see more of the fish rubbing their gills against objects in aquarium.
Being that the fish looks otherwise healthy, is eating and acting otherwise normal, you can eliminate ( for the most part) this being bacterial.
Given the clearer picture-- it doesn't look as red around the gill area. Actually, it looks like a tumor or lymphocystis. Obviously, there is no cure for a tumor and lymphocystis, being viral, has no "cure". However, the later can be controlled with good water quality, nutrition, low stress. Being that you had an issue recently with water quality, if this showed up afterwords, it will point more to lympho.
About 2 hours after posting this the fish was dead. She was buried in my yard. RIP
. Anyways, I examined the mass. It immediately gave way to blood and puss when I poked it with a toothpick. Also, please see her very inflammed egg tube and anus (if thats what you call it). I would really like to know what this was... anyways here are some good pics
WARNING DEAD FISH
Inflammed egg tube:
Hi Discusluv and others -- I wanted to provide an update on the fish's health. I will include pictures at the end. I am worried for my other gymnos now and am looking for a proactive approach to fix this issue. I have been trying to minimize stress by keeping water clean with large weekly water changes.
To summarize, this disease has had a lifecycle of its own and my fish isn't doing too great. The mass in her gill continued to grow. It started out as pink and relatively intact and smooth -- very fleshy. Once it grew it turned white, stringy, and mucousy. When it was at its biggest point, she was struggling to breathe, often spending time gasping at the surface.
The mass then started to get smaller and for some time, I had hoped she would make it through this. While the mass is still there, it is much less noticeable. Unfortunately, the disease has progressed to different symptoms. Her scales are starting to protrude (not as pronounced as Dropsy but still there), her fins are starting to fray, and she has a white spot on her back which I believe is some kind of sore. She is acting very lethargic and I don't think she has much time left.
Also, after doing a water change the other day, I noticed my other gymnogeophagus were rubbing themselves on the substrate and decor, which was the first symptom I noticed on my very sick female. While this behavior has subsided, I am still stressed out as I am proud of growing these fish and am attached to them. Are there any preliminary measures I can take such as aquarium salt in the case that the rest of the gymnos are sick with this unknown disease?
Here are some update pics: