Not seeing the "red sores" that usually accompany uronema. I'm leaning gram negative bacterial infection. It's an extremely quick killer and is not usually infectious, thus your other fish appears ok. The antibiotics used to treat can take quite awhile to do some good. Remember they don't "cure" they just help give the fish's immune system time to gear up and fight the infection. I've had really positive results using Nitrofuracine Green Powder (NFG). It seems to get into the fish's system quicker and more completely. Sorry for your losses.
From
@Humblefish
Bacterial infections:
Symptoms - Sometimes it's self-describing: Popeye/cloudy eyes, fin & tail rot, dropsy (bloated fish), etc. But some other bacterial infections, such as furunculosis, hemorrhagic septicemia, etc., can have varying visible symptoms. Any redness or open sores/wounds on a fish should be viewed with suspicion.
Also, a white film or fungus-looking growth may denote a bacterial infection. It’s important to note that in many cases a bacterial infection is usually
secondary in nature to a parasitic infestation such as ich, meaning if a fish has been battling ich for a while then his immune system has been lowered. This makes infection more likely for many opportunistic, harmful bacteria.
Treatment options - Broad spectrum antibiotic medication i.e. one that treats
both gram-positive and gram-negative bacterial diseases. Examples of this include
Furan-2, Kanamycin aka
Seachem Kanaplex,
Nitrofuracin Green Powder,
Triple Sulfa Powder, or a
combination of using both Erythromycin & Minocycline. The latter can be accomplished (albeit expensively) by using freshwater
Maracyn 1 & 2 and then doubling the dosage for saltwater use. When battling a particularly nasty bacterial infection, combining
Furan-2, Kanaplex and metronidazole (ex.
Seachem MetroPlex) can be very effective (and safe).
Props to “hedgedrew” for enlightening me of this.
