I wasn't able to find information about 'next steps'. Apologies for any bad spelling etc. I took far too long writing this and just needed to give up looking for spellings of medications/diseases just because they had the red squiggle...
Background: I believe I have a tank pretty heavily infected with Neon Tetra Disease. I had been treating as if some had cotton mouth, but it has clearly spread and gotten worse. Thanks to a previous post on here with pictures I finally realized it's more systemic and that is why medications didn't help. (maracyn, paracleanse, salt, methylene blue dips, kanaplex, pima fix...might have missed one or two)
This is a 20 long. I've had it set up with these fish for about a year. I lost a couple guppies along the way but figured that was just from inbreeding/random illness. I've never had ammonia issues and honestly I barely had the tank "cycled" about a month ago for the first time, it is heavily planted enough and has a light enough load that it honestly may have just been from the easy green the week before. (20 gallon, canister, air stone, variety of foods. Stocked with 2 male endlers, 2 male guppies, 11 neon tetras, ~6 ottos...they're great at hiding so I may have lost one but I don't THINK so.)
I am now treating this as a hospice tank. I am going to let the fish in there live out their lives until they look ill enough (and slow down enough) for me to catch and euthanize. Several tetras appear to have cotton mouth that can't be treated so I'm guessing it isn't from columnaris. One started flopping on his side. One has the full body fungus/shedding/rot look but they are all still fast as lightning and I don't want to over stress all of them if they're all likely to pass regardless.
(Corey's video says it's caused by bacteria, Aquarium Nexus says protozoan parasite*...I've tried to put both terms in below because either way I just need to know how to not spread it)
Questions:
How long can the parasite/bacteria live without a host? Once all the fish have passed, can the tank be run to keep the plants alive and have the parasite/bacteria die off with hosts then be restocked? (I remove fish as soon as I find them, I've never noticed one that looked like it had been eaten so it is spreading in the water somehow)
Can the parasite/bacteria spread by gravel vac? Would rinsing it between tanks help? Does bleach help? What about other supplies like nets?
If I need to move plants/decor/etc to another tank would treating with hydrogen peroxide help? Bleach? Letting it thoroughly dry out? Steaming? Nothing is worth the risk? (I have to assume that like ich it will eventually die on its own, I just don't know what it would take to get to that point).
Anything else I didn't think of or any other advice?
Thank you for being such an amazing community that I'm not really knowledgeable enough to contribute information to. Hopefully I can help someone with similar questions down the road by posting this for them to find!
*Pleistophora hyphessobryconis is a species of microsporidian, a group of single-celled parasites closely related to fungi. This species is commonly known to cause a disease in freshwater fish called “Neon Tetra Disease” (NTD). https://www.aquariumnexus.com/neon-tetra-disease/?unapproved=21617&moderation-hash=187643f3e498e0788e6093b393e64b94#comment-21617