Sorry, another off topic question about fish

Hey y'all

I have a fish tank along with my lotls. Its predominantly a feeder guppy tank but we have a couple of bristlenose plecos and four cardinal tetras in there too. Oh and three corydoras. I think one of our cardinals has dropsy.

Its gotten exceptionally fat. And some of its scales protude - not all. I've read up on dropsy and it kind of fits the part -swelling and some scales protuding. But from what I've read all the scales should stick out like a pine cone and it doesn't on this gal and shes perfectly active and eating and socialising. Which with dropsy she shouldn't be eating and shouldn't be very social.

And from what I've read dropsy is caused by bad conditions except the tank has been cycled long ago and all the parameters are perfectly fine. Ammonia and nitrite 0 nitrates never get above 40ppm and ph is generally about 6.8. Temp is 24. The only think I can think of is we added two new corydoras from a reputable source - would they have brought in the disease?

I'm very confused. Should I treat the tank with melafix (I read melafix can be a treatment of dropsy) or should I just wait it out and she if she gets worse? We don't want to lose our pretty gal. Would it be detrimental to the tank if I treat with melafix for no reason? Will dropsy affect the guppies and therefore should they not be feed to my lotls at all?? Obviously I wouldn't feed any to my lotls till they have been re-quaratined after treatment. Am I going to lose all my fish?

This has really frustrated and disappointed me. I can't see any reason my fish should be getting ill!

A picture would be really helpful, there are lots of reasons why fish swell up, dropsy is one of them but it could be organ failure or an enlarged liver from a bad diet. cancer of the ovaries or egg retention can also make female fish look bloated. unless it is a bacterial disease it might not be bothering her at all, like you say dropsy causes the pine cone effect on the scales so if there's none of that it might be best to keep an eye on her to make sure its not causing her any discomfort.

Thank you for replying. She does have some of the pine cone effect as in she has afew scales that do protude just not heaps. It just makes her look fluffy. She gets a variety diet - quality JBL flakes, daphnia, microworms, bloodworms, microganules etc. She doesn't appear to be in any pain or discomfort either - she's acting like normal and is very social with all the other fish. I thought she was just ready to drop some eggs but the "fluffy" look with her scales had me worried.

And as for a picture - it's very hard to get one that shows her how she is. If I take one side on you can't see it.