Weak Stock?

[Talvari]

55 gallon planted tank, running for more than two years.
370gph canister filter (CF400UV truaqua)
50% weekly pwc.
Dose once weekly with liquid ferts.
Dose once weekly with organic CO2.

Tested with API Freshwater Master kit:
Ammonia: 0
NitrIte: 0
NitrAte: .5

Stock:
1 Hifin Pleco
1 Pearl Gourami
1 Blue Ram
2 Bristlenose Pleco
3 Pineapple Swordtails (+ fry)
4 Otocinclus
4 Nerite Snails
5 Peppered Corys
10 Cherry Barbs
7 Bloodfin Tetra

I have not added any fish in months.

Problem: I started off with 10 bloodfin tetra in January. They were pretty small to start with, only about an inch long. Now they are almost double that. I lost one because it jumped out of the tank. Four months ago, one of the biggest ones started to not open its mouth as much. Then it stopped opening its mouth at all. It did not look red or fuzzy... Just puffy. A few weeks later, another one started with the same thing. I tried quarantining them but it was too late... They could not eat and were having a hard time breathing, so I euthanized them.

Now I just got done cleaning the tank and saw that another one has patches of discoloration on its side in a saddle-shaped mark. He still moving around ok, but it definitely looks odd.

Thing is.... all my other fish are fine. My cherry barb females look full to bursting with eggs, my bristlenose just spawned...

So could it just be a weak stock? I got them all almost at the exact same time from the same place.

 

[Oceangirl]

Did it look like this?

Neon Tetra Disease; Sporozoan Fish Infection


Not just neons can carry the disease, Neon tetra can effect all the tetras and some other fish. I lost an entire school of Red Sempra tetras, Then all my Neons. I'd quarantine, and try medication. It also could be some type of mouth fungus, I had the same thing on my molly this past two weeks. I dipped her once per day in methylene blue and aquarium salt, and then treated with pimafix for good measure, gone it 1 week. I like methylene blue, because its a great first attack, dip for new fish, and I quarantine all my fish in it now. No disease.

Did you add any new plants before this happened? Change a water source?

 

[Talvari]

I haven't added anything new, fish or plants, in months. Ive been using the same water source for more than a year, now, too. I don't feed live foods, either.

It kind of looks like that on this last one, except hes still schooling and not showing any other symptoms of NTS.

Maybe it could have been mouth fungus on the first two... but why would this only be affecting the bloodfins and none of the others?

 

[Oceangirl]

Neon Tetra and False Neon Tetra are very yucky. Do you have a quarantine tank? I'd move your little buddies to a QT then treat with a broad spectrum such as the Methylene Blue, Melafix, Pimafix, and perhaps Aquarium salt. I know some might throw a fuss about the salt, but I really like using it. I've used it on my Mollies, Black neons, Neons, Platy, Bronze cory cat (As a precaution to getting rid of anything they may be hiding and only for a few days), along with the Methylene blue for baths. I'd see if you can find Methylene blue, or quick cure, make sure to move them before treating almost all meds will throw your tank balance out of whack.

I also just bonked myself in the head, you have a pleco right? I read somewhere here on the forum, they like to suck the slime off sleeping fish! They maybe your little devil weakening the fish and in their weakened state succumb to disease. I have never had one, and was thinking of getting one. Till I read that somewhere on here.
I'd Qt them still and treat with what you have on hand for broad spectrum.