Concerned about Rosy Tetra

PolyVinalDistillate · Mar 4, 2026

Hi - I have 5 Rosy Tetra, and one has developed a white patch - seemingly under the scales - on its back.

Tank is well planted - to the point where Nitrate is next to zero these days. Nitrite is zero, Total hardness ia about 75 ppm, total Alkalinity about 80 ppm, Carbonate about 80 ppm and pH about 7.2 on latest test with test strip. Tank temperature is about 24 - 25 deg C. Tank mates are two peppered corys, 4 rosy tetra and a red honey gourami. Tank volume is 60-odd litres.

The fish in question is acting quite normally - but as you can see, the patch is fairly pronounced.

As the current tank is an upgrade from a ~25 litre tank several months back, I have both the filter that came with the 60 litre tank and the old filter still operational (I never took the old filter out of the new tank after transferring everything to the new tank), so I have set aside a 10 L bucket of water with some tapsafe and a heater in it in preparation to move over the small filter and use the bucket as a quarantine tank if deemed necessary.

Does anyone know what the ailment is? And what the best treatment would be? I intend to pop down to the local aquarium shop - but would like other opiniolns from people I know are in the know before I go somewhere that has a motive driven by sales!

Cheers : D

anewbie · Mar 4, 2026

From pictures it is hard to tell but it might have scraped itself if there is hard scape. If that is the case fungus will grow on it until it heals. The fungus is harmless and does not require treatment. It could be something else like a bacteria infection but that is harder to diagnose from a picture.

PolyVinalDistillate · Mar 13, 2026

The mark appeared to be under the scales. I took the photos to the local aquarium shop and the fella there immediately said "yep - fungus". He suggested a broad antifungal treatment that I've finished the course of today. The white patch appears to have faded, though it's still visible. The fish remains seemingly perfectly healthy though : )

anewbie · Mar 13, 2026

While you are welcome to spend money on meds in general as i said fungus will grow on a wound and as the wound heals it will get worse and then vanish. There are of course exceptions and other causes for fungus that sometime but rarely require active treatment (passive treatment includes keeping the water very clean and sometime a bit of warmth). Stores love to sell meds as they make lots of money off of the various witch doctor's hocus pocus.

For parasites such as ick the situation is a bit different and meds are often required to kill invaders though salt also works as long as not used with in a tank with plants; it is nto clear to myself if meds or salt is less stressful to the fish and of course some species of fish are intolerable to even a small amount of salt as well as some not doing well when dosed with methane blue.

PolyVinalDistillate · Mar 13, 2026

anewbie said:
While you are welcome to spend money on meds in general as i said fungus will grow on a wound and as the wound heals it will get worse and then vanish. There are of course exceptions and other causes for fungus that sometime but rarely require active treatment (passive treatment includes keeping the water very clean and sometime a bit of warmth). Stores love to sell meds as they make lots of money off of the various witch doctor's hocus pocus.

For parasites such as ick the situation is a bit different and meds are often required to kill invaders though salt also works as long as not used with in a tank with plants; it is nto clear to myself if meds or salt is less stressful to the fish and of course some species of fish are intolerable to even a small amount of salt as well as some not doing well when dosed with methane blue.

I saw your message after I'd bought the medication. However, the treatment sold was quite cheap, and it's not something I've needed before - so not going to be used on a regular basis. As such, I'd rather treat than not in case it wasn't as benign as you suspected.

If I'd had a unanimous response from a few people before I bought the meds, I might have held off. Either way, looks like a recovering fish now, and that's the important thing : )

Thanks for your response though : D