Sick angelfish, bulging side

A few weeks ago, our angelfish developed a small bump on one side of her body as well as some redness on their head. After only a few days it grew to become a very noticeable bulge on one side. Immediately we began doing water changes which seemed to help at first but then it continued growing, even appearing on the other side of the angelfishes body. We are going to set up a quarantine tank but are unsure of how to treat the fish. The fish is a female and we think may be egg bound. The fish used to have an active partner but only a few months ago that fish passed away. We also are thinking there may be some kind of disease, or it could also be a tumor? We have used salt so far in case of disease, but are considering epsom salt, fasting, or fish medication. The fish is housed in 70 gallons with other tropical fish, most of which seem to be fine, however some tetras have been having small swimming issues and are experiencing fin rot. I haven't noticed any swimming problems in the angelfish and they have a pretty good appetite. Any help with what this could be or treatment would be appreciated, thanks! I also uploaded a photo of the side of the fish

Hi and welcome to the forum

The angelfish is not egg bound and the lump is too high up for the organs and grew too fast for a tumour, so it is probably a cyst. Unfortunately there is not much you can do for internal problems in fish and cysts and tumours are always fatal. The best thing is to euthanize it.

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If you can post pictures of the tetras with clamped fins we might be able to help with them.

Clamped fins and fin rot are normally caused by bacteria or protozoans getting into damaged tissue. Try doing a 75% water change and gravel clean the substrate each day for a week and see if that helps. Make sure any new water is free of chlorine/ chloramine before it is added to the tank.

If there is no improvement after a week of water changes you might need to treat the tank but post pictures and do water changes first.