It may "not" be septicemia, so it might be a good idea to get a test done, at a veterinary university, or some lab where they can check for it.
If it is septicemia, I (personally) would euthanize, and sterilize the entire tank and filter system, and anything that touched the water before adding any new fish.
But I tend to do that, when faced with a disease that can easily become epidemic.
I just received some wild fish, and along with a few ick spots, I noticed one with cloudy eyes. I am treating the tank for ick, with 18 gallons of sea water added, but the plan was to euthanize the bacteria infected fish the next day, before it spread. Luckily it jumped out during the night and saved me the trouble.
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I don't euthanize for something simple like ick, but other more difficult diseases cause a dilemma, especially now, where meds are impossible to get on the island.
I have one more cichlid that appears to have Lymphocistis, and I am contemplating euthanizing it for the same reasons. Lymph is viral, and virus's are not really treatable.
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It appears to be handling well, and maybe its immune system will fight it off, but the thought of it spreading, is the main concern and may not be worth the damage it could do long term to others in the tank.