sick cardinals

[plaalye]

This 20 gal tank has been running and healthy for over a year, no new arrivals. It is a little overstocked but i keep up with the water changes and keep the nitrates around 20. I have just set up a 29gal tank with the intention of moving these fish to it. 2 days ago noticed one of my threadfins looking poor and with further inspection found that a few of the cardinals had cottony patches, maybe a mm in diameter. One of them also has a raised area, looks like his scales are lifting a little. I euthanized the threadfin as he was suffering and not going to make it. None of the other inhabitants(khulis, marginatus pencilfish, cories, another lone threadfin) are exhibiting symptoms yet. One of my crystal red shrimp died after the first dose of meds, not sure if it's related. I'm treating with Kanamycin, it's the second day of the second dose. It doesn't seem to be getting better, or worse. Here's a few pics, not very good but you may be able to see what I've described. Nitrates after last water change were 15. Any help with diagnosis and treatment would be greatly appreciated. Thanks!

[Diana]

I am not sure what a single white spot like that is.
I would do more water changes, and keep the nitrate under 10 ppm, though.

[plaalye]

Thanks Diana. They seam to be doing fine other than the spots and raised areas. The threadfin that died didn't show any of this, he just looked old and ragged. All of the other inhabitants seem fine also. I'm racking my brain trying to figure out what it is, whether it's bacterial, fungal, or even a parasite? Should I raise or lower the temp? I'm going to keep the water as clean as I can and see what happens.

[Diana]

Wait and see seems to be the only answer sometimes.

Fungi usually do not attack healthy tissue. More often a fungus will grow at the site of an injury, on dead tissue.

Some bacterial diseases can look like fungus, and may have a common name that suggests fungus, but are actually bacterial.

There are no meds that treat viral diseases.

If you want to treat with anything it may be that antibiotics are the best gamble, but clean water can go a long way toward helping the fish to heal.