20 Gallon Tank Help!! Cory has red mark on the side of its face, unsure if wound or disease.


Hi everyone, this is an unfortunate occasion for my first post but here we are! I noticed this red blotch on my cory's face about an hour ago, and I'm certain that it was not there 7 hours ago. I know the pictures aren't great, sorry! The water is kind of dark due to tannins from driftwood.
I lost a cory from the same store to hemorrhagic septicemia/red blotch disease(I think these are the same thing?) about two months ago but haven't seen it in any other fish in the tank. That also looked very different than this, and I saw some other threads with similar pictures saying that it's possibly just a wound, but those also didn't look exactly like my fish so I thought it would be best to just check and see if anyone had any advice either way. I have Furan-2, Kanaplex, and Melafix. I'm definitely stressing out about it but I didn't want to medicate if I wasn't sure it would help. But if it's infectious, I really want to do something ASAP!!! I unfortunately do not have a quarantine tank available (except for a 1 gallon one but I don't want to use it and cause stress/isolation unless it's very necessary) Thank you for any help you can offer!!!

Emergency template:
What is the water volume of the tank? 20 gallons
How long has the tank been running? At least a year, I think since August of last year
Does it have a filter? Yes, 600L/hr with a sponge and Seachem de-nitrate
Does it have a heater? Yes
What is the water temperature? 75f
What is the entire stocking of this tank? (Please list all fish and inverts.) 4 cories, 5 danios, 1 dwarf gourami, a bajillion ramshorn/malaysian trumpet snails, one nerite snail

How often do you change the water? Every week and a half/two weeks
How much of the water do you change? 25%
What do you use to treat your water? Seachem prime
Do you vacuum the substrate or just the water? yes I vacuum

*Parameters - Very Important
Did you cycle your tank before adding fish? yes
What do you use to test the water? API master test kit
What are your parameters? We need to know the exact numbers, not just “fine” or “safe”.
These were readings before I did a 30-40-ish% water change. I can update tomorrow if needed and will probably do another water change then.
Ammonia: 0-0.25 (can't tell between the two lowest on the scale)
Nitrite: 0
Nitrate: 0-5 (same problem as ammonia)
pH: 7.8 (I've heard this is high for cories but it is stable, trying to slowly lower it with driftwood)

How often do you feed your fish? Pretty much daily, sometimes twice a day or skip a day
How much do you feed your fish? Depends on the food, I have a little spoon that's probably about a teaspoon and for pellets and brine shrimp I use less than 1/4 of it. I also have homemade food that is just kind of in chunks and when I use that I usually crumble up the amount of one or two jelly beans in size. I also sometimes give them a leaf of spinach or kale but haven't done that in a while.
What brand of food do you feed your fish? SF frozen brine shrimp, King Fish little pellets, Sea Veggies seaweed and occasionally Aqueon flakes or bottom feeder pellets(these don't work as well for this tank though). I have a homemade mixture that is made with leafy greens, zucchini, ginger, garlic, the above fish foods, and an egg with the eggshell blended in- the eggshell is because I also have mystery snails in another tank and this is the food I use for them. I was thinking it's possible that a bit of eggshell cut inside its mouth, but I've fed them this food for over two months without any problems.
Do you feed frozen or freeze-dried foods? Frozen shrimp, pellets are dried but I don't think freeze dried? I don't typically soak them before I feed them.

Illness & Symptoms
How long have you had this fish? At least 3 months, possibly 4 (I can't tell them apart and I got them a few weeks in between)
How long ago did you first notice these symptoms? An hour or two ago(11pm). I looked at this tank throughout the day starting at around 1 pm and am 99% sure that this wasn't here up until 6-7pm.
In a few words, can you explain the symptoms? Red blotch as seen in the pictures, from its left eye to its mouth. It's not on the other side or anywhere else on its body. Its face/gills are kind of pink but I can't tell if that's normal albino coloration and especially when I'm freaked out it seems like a problem lol. Swimming and eating completely normally.
Have you started any treatment for the illness? Just a water change
Was your fish physically ill or injured upon purchase? No
How has its behavior and appearance changed, if at all? The appearance has changed as described in the symptoms but it's acting completely normal, swimming all around and poking at the bottom as usual.

Please let me know what you think is going on, and what I can do to help it!! Thanks so much



I don't have a lot of experience with this particular illness, but it does look like a bloodspot. Illnesses can look different in different fish, so it could absolutely be what your other one had.
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