Serpae Tetra close to dying

[V3rmilion]

So, I've posted something before saying about how my Serpae tetra are giant fun-nippers. One of them is looking so beat up to the point of dying. He swims sort of at a slant, he's lost a lot of color, his fins are all ragged (all of the fishes' fins are), he rarely eats, he has black specks on his body, and his lips are all puffed up.

My water parameters are:
Temperature: 80°F (26.7°C)
pH: 7.5
Nitrate: around 20 ppm
Nitrite: 0 ppm
KH: 40 ppm
GH: 180 ppm
Ammonia: on the 'Safe' section on my tester

I have 3 Amano Shrimp, a Moss ball, and a heater, all in a 10 gallon. The size of the tank is most likely the problem, since I read that they need at least 20 gallons after I bought them. I don't want to rush to euthanasia, but I also don't have a quarantine tank. If anyone could help, it's greatly appreciated

 

[Derekshatch]

Ya you need a way bigger tank. How many tetras are in the tank?

 

[Derekshatch]

I have tetras and danios in a 30 gallon and they still fin nip a little it so a 10 gallon is way too small. When i first got my tetras they din nipped one small danio and he quickly healed because he was in a bigger tank and could hide until he was better
A quarantine tank is your best option.

 

[seangee]

Lots of plants and hiding places. Daily water changes of 50-75% while the fins heal.

 

[Retired Viking]

Just a thought but You could try and make your own quarantine tank by running an air line off you tank to a container like a bucket, it would depend on how warm it is where you are at since you probably do not have a spare tank heater. T connections for air lines a cheap. That would be temporary but give him time to heal.

 

[Byron]

In your older thread on this species, two of us responded and both said this was going to occur. This species must be in a group of 10-12 (or more) and in a 30g tank minimum for this group of 10-12 alone.

The fish in the photos is in very bad shape, and it may be more than just fin nipping. If this were me, i would euthanize this fish, it is much less cruel than even trying to cure it in a QT.

Going forward, the five remaining Serpae will obviously continue this with the next fish they select to bully.

 

[V3rmilion]

Ok, all of you have been very helpful, and I should probably go with @Byron 's option and euthanize the fish because it's in very bad condition. I will also try and regime some of them since the nipping will just continue on.