Update!
We are now in day 1.5 of treatment. I bought a 5 gal starter kit to use as a quarantine tank, but the hanger filter was too power for the little guy. The filter did not have any flow adjustments, so I moved him back to the main tank. Yesterday I did a 50% water change and added API® FIN & BODY CURE POWDER. This morning I notice the fungal infection grew. It was then covering both sides of the tail. The eye remained the same condition. Today I've done a 80% water change, continuing with the fin & body cure powder. It looks like the fin and body powder is more for bacterial infection, so I've added Pimafix for the fungal infection. However; I think due to the weight of the fungus growing on the tail it started to tear off. Just a few mins ago the majority of the tail has fallen off. I've remove the fungus infected tail from the tank. I've also raised the water temp from 74°F to 76°F. Tomorrow I plan to do a 25 - 50% water change and continue with both fin and body powder and Pimafix.
The nine neon tetra and the other two panda corys look healthy and are active. I'm not seeing any stressful behaviors.
Nine hours after the water change the water is currently
nitrate - 0
Nitrite - 0
GH - 200
KH - 40
ph - 6.8 / 7
Chlorine - 0
ammonia - 0
(tested with Aquarium co-op test strips)
I've attached a photo of the tail loss. Google has me hopeful that it will grow back.
P.S.
The three Corys are named Larry, Curly and Moe. The one that is giving me all the trouble is Curly.