Sick Spotted Cory, Can't Swim, Laying on Back

[Satyricon553]

First, my parameters:

38 Gallon.
Been cycled for 2 or 3 weeks.
Water test this morning showed 0 ammonia, 0 nitrite, and 30ish nitrate.
My tap water has 10 nitrate, today was water change day.
I have 8 neon tetras, 6 (5 if this goes south) spotted corys, 6 long fin zebra danios, 10 ghost shrimp, a few pest snails, and 1 assassin snail.

Last week I changed my substrate from gravel to eco-complete. There was no change in my water. Ammonia didn't spike, Nitrite didn't spike. Nitrate has seemed to rise a little quicker after changing, but that might be my imagination.

When I woke up this morning, one of my catfish was floating on its back at the top of the tank.

I went to scoop him out because I assumed he was dead. He wasn't. He swam away from me but ended up back on his back at the top of the tank. He's breathing very heavily.

Here is a video of him struggling to swim.

Sick fish - YouTube

Any advice? He looks like he is having a horrible time. Should I throw him in the freezer to put him out of his misery or could he make it?

I did a 50% water change, but he's still floating and struggling.

 

[Satyricon553]

(S)he died.

Anyone have a guess on what could have happened?

 

[jlk]

I am sorry about your fish Did you cycle with him in the tank or was he just purchased in the past 2 weeks after the tank cycled?

 

[LyndaB]

That's a lot of fish for a newly cycled tank.

Corys are sensitive and shouldn't be added to new tanks.

Freezing fish is not exactly a good way to put them out of their misery. You could euthanize with clove oil first, then freeze.

 

[foster53]

Like Lynda said,Use clove oil to euthenize the fish. In my opinion its the most humane way!!