sick cardinal, help id disease please!

[leslens]

Hi, firstly im not sure where to post a sick cardinal tetra thread
this is the closest i can find so mods pls move it appropriately if deemed unsuitable at this place.
can any expert id this disease?
is this tail rot?
i have been getting sporadic seemingly healthy fish being struck down with this disease. The white area usually starts on the dorsal fin, tail fin in some cases. Once it hits the body, the fish drops dead usually
this fish shown here is already up lorry liao 1-2 days after i found it like this despite isolation and treatment with anti-tail rot med from ocean free
any comments well appreciated

[Quixotic]

Can't really tell from the picture, but maybe it is just me.

However, if it is indeed fin rot, these are symptoms that normally show up when there are issues with water/tank conditions.

What are the dimensions of your tank? What kind of filtration are you running on (brand or specs)? What is the bioload like (how many fishes are there and what are they)? How long have you set up the tank before introducing the fishes? We may be able to provide better opinions if there are more information about your setup.

In any case, you need to ensure there are no problems with water/tank conditions (pH, ammonia, nitrite, nitrate) in the first place. Proceed with medication once issues with water/tank conditions are addressed.

No medication is going to help if the conditions are not well in the first place.