Colu

I agree looks like I would keep treating with ick X treat for 3 days after you see the last spots I would also add a Small amount of aquarium salt 1 table spoon for 10 gallons as ich causes massive electrolyte loss and the salt will add back in essential electrolytes @CaptKirkland

It difficult to diagnose what's going on off your pictures usually when you get odd deaths every now then the fish start to gradually die over a long period of time it's more likely to be a parasitic infection columnaris causes mass mortality in any were from 24hr to 7days depending on the strain and spreads more quickly at higher have you notice any rapid breathing listlessness hanging near the surface flashing spitting food out sunken belly @GinkoTracks

Looks like the start of a tumor they are really common due to inbreeding what I would do is add some Indian almond leaves as they have antibacterial and antifungal properties depending on the quality of the leaves you might have to add one leaf per gallon to get a beneficial effect and I would add some aquarium salt 1 table spoon for 3 gallons for a week and just monitor @John1101

It could be damage to the cornea what I would recommend is keep good water quality make sure you have no ammonia nitrite low nitrates keep the salt at 1 table spoon for 3 gallons and monitor it might heal give time or you could be left with permanent damage to the eye @ChrisATL2

No I don't treat during quarantine unless I noticed any symptoms I usually just monitor for 4 weeks

You just add it once on day one and let it marinate for one week

I would lower the water level if possible to relieve some of the pressure off the glass until you can replace the tank @Trop65

I would leave it at least another week it not uncommon for fish exhibiting symptoms of Dropys to have a relapse once reintroduce back the main tank if you haven't solved the initial cause such as stress caused by poor water quality bullying poor diet will all be stresser on the immune system that can lead to secondary infections or kidney infection

it looks like it might have been a case of swim bladder if you not seeing any symptoms in your other fish I think you should be fine now

I feed mine a combination of EBO spirulina tabs spirulina paste plankton tabs bugbite pleco formula pellets cucumber blanch spinach and lettuce and frozen blood worms

I was just thinking of the salt baths as your treating with maracyn I would use tap water

I think the growth on his mouth stopped him from eating ultimately lead to his death in this case

Maybe @mountaintoppufferkeepercan help you id your puffers

Great write up lots of useful information It's a common misconception that Neon tetra disease only affects neon tetras it has also been found in angel fish goldfish danios Rasboras barbs other types of Tetras such as cardinals rummy nose tetras and guppies as well it has symptoms that could be mistaken for other disease that why I think a lot people misdiagnose this disease @ZoeyFish

Did it have a sunken belly as it could be that he was struggling to eat and got progressively weaken and that what kill it

Doesn't look like a parasitic infection possible bacterial infections what I would is treat with medication with a different active ingredient I would do a course of maracyn2 in food active ingredient minocycline is a broad spectrum antibiotic treatment and also has anti-inflammatory properties feeding a small amount twice a day for 7 days and I would keep the level of salt at 1 table spoon for 5 gallons@Goshfush

If it's anchor worms remove the fish straight to away to a quarantine tank to provent the female anchor worms from releasing it's eggs then i would treat with hikari cyropro paracleanse won't have any effect on anchor worms @CJs Aquatics

Yes you can I usually use tank water because it has the same parameters and temperature so it's less stressful and just top off the tank @MattyM

It's difficult to tell off your picture if these are anchor worms they typically borrow into the skin of your fish he's some pictures of anchor worms for comparison @CJs Aquatics

If it's just affecting one eye it's more than likely caused by an injury what I would do is Epsom salt baths 1 table spoon for 2 gallons for no more than 15 minutes for 5 days that should help reduce the swelling and finish the course of maracyn @MattyM

As most Otto's are wild caught it could be encapsulated nematode worm or an injury or fluid filled lump what I would do is add some Indian almond leaves as they have antibacterial and antifungal properties depending on the quality you might have to add one leaf per gallon to get a beneficial effect and would add a Small amount of aquarium salt 1 table spoon for 10 gallons just incase it's a fluid filled lump the salt will help reduce any possible fluid buildup and monitor for a couple of days if you notice it getting worse give use an update

Velvet derives some nutrition from the host it also photosynthetic so it get nutrition from light some recommend blacking the tank out during treatment The most effective treatment is Fritz copper safe you need to keep the copper levels at 2ppm so you will also need a copper test kit typically it will take a month of treatment you need to dose copper safe once and let it marinate you will only have to add more if you do a water change to get the level back to 2ppm copper safe is harmful to shrimp and snails if you have either I would remove the fish and treat them in quarantine if you can @mynameisnobody

Have you got a better picture what are your water parameters ammonia nitrite nitrate etc with what your describing it could also be swim bladder issue has your fish got pineconing or any other symptoms @smvian_memes

The most effective treatment for columnaris is a combination of kanaplex and jungal fungus clear fizz tabs containing nitrofurazone following this treatment plan API furan 2 has been discontinued it can take two full course of treatment back to back @saphbettas I would keep treating with kanaplex and order jungal fungus clear fizz tabs when they arrive I would do a full course of kanaplex and jungal fungus clear fizz tabs following this treatment plan @saphbettas

Most Otto's are wild caught I would always recommend quarantining them and treating for parasites preferably In a well seasoned tank if that isn't an option you could leave rocks or wood under a bright light or in a tub out side to grow biofilm and add new piece's each day to the tank