Cardinal Tetra - Bloating/obese, Buoyancy Problems, *purple Marks On Underside*

I've noticed quite a bit of variation in my 7 cardinal tetra, not just in size (1 longer-standing large one, 1 similar-sized large one that is also very obese, 1 runt of probably 10% bodymass of the latter, and the rest all roughly the same), but also in patterning/colouring. Several also have a navy-blue hue in their red colouring, depending on the angle viewed at. This is the first species I've had with such variation but, with the situation among the cardinals having been settled since their last fatality 6 months ago, realised it must be normal for them.

A week or so ago, the obese/bloated female developed a white pimple on her caudal fin but it disappeared within a day or two.  She also had a few purple-like markings on her large white underside, possibly near the fins. My recollection is that the short-lived pygmy cories developed these, often in conjunction with bloating. Today, however, a white flat mark has appeared on her caudal fin in the same location as the white pimple previously, she's struggling to maintain buoyancy (swimming harder to maintain horizontal position, with her tail naturally tending to go upwards) and the purple-like markings much more visible, especially on one side.

I'm struggling to obtain video footage but, in the interim, any thoughts on what this might be? A bacterial infection affecting her swimbladder or viral septicaemia have popped into my head as possibilities.  When googling the description of the purple markings on fish, this picture on a human popped up and is the nearest equivalent I can find.

Edited to add: https:///youtu.be/s7EQew5Wouc and https:///youtu.be/822C7Zp68EY (fish near bottom of video)


<a href="https://www.youtube.com/watch?v=s7EQew5Wouc" target="_blank">http://www.youtube.com/watch?v=s7EQew5Wouc</a>


<a href="https://www.youtube.com/watch?v=822C7Zp68EY" target="_blank">http://www.youtube.com/watch?v=822C7Zp68EY</a>

In the first clip is it a purple patch on the left hand side of the fish, underneath the red stripe?
It looks slightly uneven there, but it is very difficult to tell what the problem could be.

How are things this morning?

I understand. I'd be doing the same thing myself.

Update: The situation has continued all day, tumbling, spiralling, etc. Colours remained bright and vivid, though. https:///youtu.be/ALJWKfVzdXA
I looked into the hospital tank late afternoon, didn't see her tumbling around, called out to her, then she came swimming/tumbling towards me and acknowledged me. Ten minutes later, I looked in, and she was "dead" at the surface, belly up. I delivered my customary little eulogy, then went to have dinner.
Returned to remove the body.  She had vanished, speed-swimming around the tank in a frenzy, then "died" again, gills not moving for over a minute. Got out the euthanasia equipment, just to be certain. My goldfish spent 22 hours in this state of long spells of hours of being dead interspersed with very short spells of frenzied activity, especially when I tried to move him, assuming he had finally died. This time, despite the ongoing vibrant colours, I wanted to spare her of this as it was now clear she was beyond the point of return. Managed to net her into the container, before pouring in the clove oil and water emulsion, and out she leapt... She's now back in the tank, upside down under a bridge ornament, and I'm simultaneously hoping nature is taking its course as I dictate and edit this...

Thanks, LF.

Went to bed last night after leaving her lying belly-up on the surface, seemingly dead for about the 4th time. I felt dreadful, being unable to bring myself to "assist" her, and lay there hoping that she wasn't suffering. I fully expected to find a decomposing/decomposed body on the tank floor this morning. Nope - she was swimming around.
The entire today so far has been a combination of these spells: https:///youtu.be/H9AuHBrN7R8 (upside down, belly-up, seemingly dead or possibly the most comfortable position for resting in) and https:///youtu.be/0tFL1J_1g0U (this was taken immediately after the video, as soon as I removed the tank lid which set her in motion).
I have no idea what's going on, other than that euthanasia is off the agenda, when seeing those vibrant colours and activity in the light of day, even if she is swimming in the bizarrest of ways. I'm not giving up on her and also feel that I absolutely need to do all I can to help her.

If I have to keep her in an isolation tank indefinitely +/- her friend for company, so be it. At the current stage, my plan is to extend the treatment course (also bearing in mind that the initial doses' effectiveness may have been impaired by active Seachem Prime in the water), with Waterlife Myxazin next. I've also contacted the uni veterinary dept for their views - they were very kind and helpful the only previous time I've contacted them in my goldfish-keeping days. [Updated: struggling to get contact with them, so am now contacting an online vet service provided by the USA that I used pre-forum days.] Of course, now that I've got out of bed 3 mornings in a row absolutely certain that she'd be dead, and additionally have got a clear plan of action in my head, I expect nature will now intervene and throw the next curveball! 

Thanks for asking, LF.  Same again.  This summarises the past few days, taken late morning: https:///youtu.be/9tfsMapxmXE

I've really begun to learn how we fishkeepers rely on one another's collective knowledge and that there's little else beyond it. No responses from the vet avenues I've tried and/or the increasingly common "passing from pillar to post" that happens these days (with willingness to help being a needle in a haystack), in contrast to what I'd hoped. However, I'm keeping my fingers crossed that some Maracyn-2/minocycline that I've ordered online to address septicaemia arrives sooner rather than later (timescale 1 week - 1 month) and can "save the day".

Check with the vet to get advice on starting treatment immediately/after water change.
I don't have any previous experience of this sort of situation, so don't feel as if I can give any specific advice.
Best of luck though.

Sorry to hear that the situation has got worse.
You've done everything that you can to try to generate a more positive outcome.