One Tetra Suddenly Afraid Of Light?

So, one of my tetras has been acting weird for the past three days. He's the biggest and one of the oldest two. None of the other inhabitants are acting strange.

My tank is being treated for ich with only heat and salt. I have been treating it for 7 days. Here are my params as of this morning:

Temperature: 31 degrees Celsius/88 degrees Fahrenheit.
Tank size: 15 gallons
Salt: 0.5 teaspoons per gallon.
PH: 6.8
Nitrates: 30
Nitrites: 0.25
Ammonia: 0
Heaters: 2 Marina 50 volts
Oxygen: 1 air stone, one bubble wall, plus water agitation from the filter.
I have leaf litter and cholla wood in my tank, and the water is slightly stained with tannins.

I am doing 25% water changes every evening.

I will be upgrading to a 45 gallon breeder tank once it's ready, but that's probably not until September or later.

Day one: It started with aggression after feeding. The fish began charging the others, bashing them in the sides. I was worried because he's the largest, but I figured he was just trying to establish dominance. I noticed him attacking a female, the one most afflicted with ich, and thought maybe it had something to do with that.

Day two: The next morning, he was gone. I searched for him and couldn't find him, but I had to go to work and didn't have time to really look. When I got home from work, I noticed that he was hiding in the log with his lights off. I inspected him and he didn't seem injured -- and when I turned the tank lights off and fed them, he came out, lit up, and ate as normal.

Day 3: Today I found him near the airstone. My tetras are never schooled when I wake up in the morning, so they were all scattered around the tank. I turned the lights on, and they all schooled, except for him. He went to the corner and dimmed his lights. I added a bit of food to see what would happen, and he ignored it. Then I turned the lights off, and he came right out and ate. I noticed he seems really bloated and heavy. After he ate, he schooled for a bit, and then hid again.

The lights are currently on because I don't want to throw everything even further out of balance. He is hiding below one of the heaters.

I just looked up and he is schooling again, but he is so dI'm and bloated. It seems like he's retaining water, not that his stomach is bloated. His eyes are slightly bulging -- however, it doesn't look like dropsy.

I have a 10 gallon I could put him in, but I don't want to move him and stress him out further and end up killing him, especially since he still has an appetite and is schooling now.

 

Popeye maybe that might explain light sensitivity. Watch out for lifted scales and if he gest them remove him imidietly.

 

So far no lifted scales, but the bloating hasn't gone down at all. He's trying to school at least, he just can't keep up with the others. Still eating, just very sluggish and definitely doesn't like light. I wonder if he was just injured while he was being aggressive the other night. He doesn't seem like he's dying... He's still trying to participate. No other fish are showing signs of this at all.

 

I found him dead this morning. The shrimp were fighting over his corpse.

Is it possible that the other tetras beat him up? Do they dispatch problematic members of their own species?

 

Hmm I don’t think the other tetras would have ganged up on him for being problematic. Much more likely that he got some sort of fast acting internal infection - possibly due to a weakened immune system from the ich. How long had you had the fish?

 

I've got a one eyed Cardinal Tetra that has absolutely no gip off the other fish whatsoever. Swims like he's got swim bladder but that's purely down to his eyesight but isn't treated any different by any of the fish.