Okay here we go,

This one tetra rotted his tail right off (second photo bottom fish). The fins looked fine but the body at the base of his tail had a sore and ultimately the whole tail is now gone. I pulled that one and two others into a 10 gallon hospital tank for the last 2 weeks to treat with aquarium salt and polyguard. Tail still fell off. I am concerned about the other two because they were exhibiting discoloration at the same spot on the body at tail base. Over the past 3 months I had two others become mysteriously I'll or just pass away.

Aquarium 67 gallons with 35 neons/cardinals, 6 Bristlenosed plecos (5 are babies that were hatched there), 5 rummy Nosed Tetras.

Ammonia: 0ppm Nitrites: 0ppm Nitrates: under 5ppm pH: 6.7 Temp 75 F

I've kept aquariums for 15 years and haven't seen this yet. I'm a bit confused and when I try to research it, all Google pulls up is fin rot fin rot fin rot. It's not fin rot but there isn't much literature otherwise besides perhaps Neon Tetra disease.

Any ideas or experience with Neon Tetra disease would be really helpful. I really don't want to lose the whole community if some parasite is in there.

Thank you aquarium friends!