Cory Catfish Dying?

[Ale_xis]

I have a little albino cory who started acting up. Earlier before feeding, he kind of swam crookedly. Just a few minutes ago, he swam again and it looked like he was drunk. He was twirling across the tank, to the surface, then twirled back to the bottom and isn't moving much... just pretty limp, but he's alive. The other 2 corys are fine, and all the other fish seem normal too, so it's just him.
I have a 10 gallon with lots of plants, filter, heater and sand (only a few pieces of small gravel and 2 small rocks). My tank is overstocked but it wasn't really my choice- they were "rescue" fish. I have 3 platys, 6 tetras, and the 3 corys.

Any idea of what this is? Could he perhaps be dying?

edit- Also, I did a water test. Ammonia and Nitrite both were 0, and their water was replaced about a week ago.

 

[techen]

Like this?

 

[Ale_xis]

At around 44 seconds is kind of what he was doing. He wasn't moving fast, just very slowly across and up and down the tank while spinning and twirling. Right now he's just sitting in the corner...

 

[techen]

Parasite, Treat with anti parasite meds. I had to put that cory down, I couldn't get rid of it and it was making the cory go brain dead. Was sad but I did what was best.

 

[Ale_xis]

Oh dear, he's on his back at the bottom... I think I may be losing him

edit- And he just flipped back over... It's too late to go to the pet store now, and tomorrow is a holiday. I'm afraid what I'm feeding them is the problem, maybe he's sick from not getting enough nutrients?

I feed them every other day both tropical fish flakes and 1-2 shrimp pellets, so all the corys eat are the pellets (they never can get the flakes).

He's not doing good at all, he tries to swim up then just sinks back down.

 

[Ale_xis]

how he is now

 

[Ale_xis]

Sadly he didn't make it I took him out and put him in an isolation tank and tried feeding him peas but he died shortly after. He was limp, did nothing when I brought him out of the water, and was not breathing so I said my goodbyes and buried him.
I hope his short life was better than the awful pet store tank he came from. I'm thinking he died of disease from the fish tank since there were 2 dead fish in that same tank. I just hope the other corys and fish are okay.

RIP Ale.

 

[eaglesaquarium]

Sorry for your loss.

 

[MrsM]

 

[mark4785]

Are these albino catfish bread specifically for their colours by some breeders or is it just a freak of nature?
 
If the former is true, it might be that the fishes colour was prioritised by the breeder over more important things like good immunity.