Considering this is the internet, you have been given some absolutely sound advice. The redness is indeed likely to be sepsis, based on your location and details in this thread, i would hazard a guess at a secondary bacterial infection with Aeromonas Hydrophilia.
Be VERY careful with this bacteria, it is Zoonotic and very common, the pattern of redness is a dead give away of it, also note your not out of the woods yet.
You MUST get a test kit, there is simply no reason or excuse not too. DO NOT feed any thing yet. Out of interest what type of filtration do you have?
I wont mention tank size etc........
I dont understand why you are holding off on the test kit, this isnt a nice have, it is absolutely essential to have one. The fact you have got several years out of the fish is simply down to pure luck, this luck has now run out.
If you cant afford a test kit, i am sorry to say you cant afford to keep the fish. I have a feeling based upon your reluctance to part with a relatively small amount of money, that you wont actually buy a new tank, like many people you will say what it takes to get help.
Your fish may looked improved at the moment, but this can often be a function of bacterial behavior and immune response. I would guess the Leukocytes have kicked in and reduced the bacterial load in the blood, however this bacteria has a habit of adapting and overwhelming the immune response.
I would not be surprised if it took a turn for the worse in a day or so, if it does then its game over. Please stop wasting time, go and get a test kit. You are making the people here work blind, they wont to help you and your obstructing that help with a passive response.
And do listen to what others have told you, it is great advice. Wash your hands well after dabbling in the aquarium, you dont want that bacteria getting into a cut in your skin or whatever
, it has been widely known to cause necrotic fasciatus in humans