Hi all, wanted to update this post as I've been able to save the remaining 5 diseased Corydoras and wanted to share my experience.
Disease Description: Disease would initially present itself as a small patch of white/grey film on the tail area of the Panda Corydoras, then rapidly spread over the entire body. When it spread to the fins, the fins would rapidly erode.
Potential Cause: This disease appeared in my aquarium after an unprecedented cold front where the temperature in the tank dropped from about 78 to 68-70 for 2-3 days. I think this is what caused it, as well as a gunked up filter that wasn't operating at full capacity.
Treatment Timeline:
Day 1 - Noticed a slight discoloration on the tail of one Panda Corydoras, but all other Corydoras looked fine and were active/eating so I didn't think much of it.
Day 2 - Initial Corydoras deteriorated rapidly with quite a large portion of the tailfin being eroded within 24 hours. I begin dosing with Ich-X and Erithromycin.
Days 3-6 - Kept dosing with Ich-X and Erithromycin, the Ich-X noticeably irritates the Corydoras and makes them constantly dart up for gulps of air. Treatment doesn't seem to be having any effect, and by this point the disease has spread to 6 Corydoras, and they're deteriorating rapidly. I'm asking for advice online by this point. One Corydoras has died at this point.
Day 7 - Bought a 10 gallon hospital tank, and set it up with a sponge filter (from main aquarium) and about a dozen miniature Catappa leaves. I dose 10 teaspoons of salt at this point (around 3 tbsp per 10 gal), and add the remaining 5 affected Corydoras after tearing apart the main aquarium.
Day 8 - Notice that one Corydoras in the main aquarium that wasn't removed the day before also exhibiting the beginning signs of symptoms (see image 1 attached). Don't have time to tear apart the aquarium, so I leave it in the tank.
Day 9 - Corydoras inside the hospital tank continue to deterioriate (see attached pictures 2-3), so slowly over 24h I increase the salt concentration to 4 tbsp per 10 gallons. At this point, I begin noticing signs of stress in the Corydoras (flashing, erratic swimming) so I stop adding salt.
Day 10 - All 5 Corydoras in the hospital tank have eroded fins and white growths over the body, so I begin medicating with Erithromycin because I figure that some type of bacterial infection would be at play with the open sores/eroded tails.
Days 11-14 - Erithromycin dosed each day, salt is kept constant at 4 TBSP per 10 gal. I feed Xtreme nano pellets to the Corydoras 2x per day. Corydoras will not touch any other food besides the Xtreme nano.
Day 15 - After 5 days of Erithromycin I did a 30% water change, and didn't replace the salt (so now back to around 3 tbsp per gallon). Only one Corydoras remains with white growths on the body, other Corydoras are showing signs of regrowth in the tails (see picture 4). Corydoras in the main tank is thankfully healed on its own without medication and hasn't spread the disease.
Day 17 - Did another 30% water change without replacing salt. Still have 1 Corydoras with slight growths on its body, but appears to continue to be improving. (See last picture attached).
In the end, I suspect it was a bacterial disease because the combination of Erithromycin + salt seemed to work out the best. Corydoras seemed to continue to deteriorate with just salt / just Erithromycin alone.
Also as a note, the Ich-X really seemed to be extremely harsh on the Corydoras and I think I'll be much more careful about dosing it with Corydoras going forward. I was dosing it because I wasn't sure if the disease was bacterial or fungal. Honestly, I think that the 1 Corydoras that I lost during this whole process might not have died if I hadn't dosed Ich-X, because that particular corydoras was noticeably stressed after dosing that med.
Thanks again to all for the advice/feedback.
