Fish Problem

[limsteel]

Was rescaping my tank and spotted a groups of Neon Tetra gill are RED... Is it Gill infection??? Even the Golden Algae Eater's gill cover small portion missing!

Carinal & RummyNose Tetra can't tell as the red blend in to the body's original colouring...

Xiao Liao! Like that how?

[PeterGwee]

Presence of ammonia or NO2...check with a test kit to confirm...do a 50% water change and add salt to reduce the effect.

[Blue Whale]

I quote u two diseases. See which one fit best.
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furunculosis (aeromonas - open lesions)

Cause:
Symptoms:
[1] - Open red sores, (ulcers) which sometimes appear as small raised bumps. A similar disease, Red Sores may appear on the side of discus fish.
Treatment
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hemmorhagic septicemia

Cause:
Symptoms:
[1] - Blood streaks without sign of skin damage. Seen in goldfish as blood streaks in the fins.
Treatment
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[DEA]

ehh
i would also say it's much more likely to be nitrite burn
occam's razor (the simpler answer is usually the correct one) applies quite well to the aquarium situation
i've killed off fish because i thought they were suffering from some disease when in reality the water was just bad

try changing the water and adding a little salt
the salt will block nitrite uptake
act fast
nitrite doesn't wait for anyone