About 6 weeks ago, I noticed what I thought was white fungus on two of my nine false juliI corydoras. One was on the mouth, and the other on the "saddle" near the dorsal fin. All Corys were acting normal and eating, but I quarantined the two and treated with Fungus Cure. Nothing changed, and as I did more reading on this forum, I began to suspect Columnaris. Not being able to get Kanaplex in my town, I ordered it but treated with Furan II in the meantime. When the Kanaplex arrived, I noticed that one more Cory in the 46-gallon display tank had the white mouth, and yet another Cory died overnight. When I examined her out of the tank, she had white lesions on her side and on her underside (wish I had snapped a photo!), she had a very hard off-white growth that looked like <1 millimeter diameter tubing coiled tightly like a rectangular pinwheel on her belly.
Feeling more certain this might be Columnaris, I moved the two from QT back to the display tank and treated the whole tank with Kanaplex (full course of 3 doses over 6 days). No change at all. The white areas on the dead Cory were definitely not fuzzy like fungus, but more lesion-like.
The two Platies and one Molly are unaffected as are 5 of the other Corys. I snapped a photo of the white mouth on one and the saddle white lesion on another (it's the smaller Cory in front) and the lesion is smaller than it started out, but you can see that the dorsal fin is only partly there.)
I don't know what else to do and would appreciate suggestions. The Corys are still acting normal and eating, but the lesions must be uncomfortable, and the affected mouths no longer have barbels. My water parameters are consistent with what they have always been. My water here is hard, and I have added crushed coral to try and improve buffer. I still use Wonder Shells.
I feed Omega One color flakes to the livebearers, and feed frozen Emerald Green, Mysis, and Brine shrimp to everyone, and also Omega One Shrimp Pellets and Veggie Rounds. I do 50% water changes, vacuuming the gravel once a week, so my nitrates are rarely above 10.
I would certainly appreciate advice/help with diagnosis from the Forum!