One cory breathing heavy :(

[InfraredDream]

Hello,

Not sure what went wrong so fast
Yesterday at feeding time all cories were active and hungry. This morning I had a quick look at the tank when turning the light on and one cory was swimming fast with weird turns up/down then went to the bottom. I was in a hurry as I had an early morning meeting and just said to the kids and my husband this cory was strange. I just came home and one of them, probably the same one is at the bottom breathing heavy, haven't seen them doing that before. And the gills look more redish then usual I will do a 25% water change, but this guy looks like it won't make it The others are fine.
Any idea what may be wrong?

[jobber]

Is this cory one of the bigger ones and gravid? It could possibly be that it just finished spawning. Breathing due to exertion of extra energy during the spawn. Hope things work out well.

[EDGE]

Something is irritating the gills if the gills are turning reddish in color. Could be anything from fine particle to parasitic to infection.

Normally, if I just got the fish from the LFS and something like this happen, I use prazipro to limit the problem. They tend to get better within a couple of days of prazi pro.

How are you doing your water change? straight tap or conditioned? added any new fish? How long have they been in the tank? temperature? gh? pH?

Also Could be the tap water causing a problem cause I have noticed a change in behavior with my older corydoras in the last 2 weeks. Not spawning behavior. Seems more skittish but eat like a pig still.

[InfraredDream]

Thanks a lot, guys!
Nothing new in this tank for months. If I don't count the new baby endlers
I leave the water to age over night or a whole day and then still use Prime in it.
These cories are with me since early Sept. and I love them a lot.
Don't think they spawned though.
The gills are just maybe a bit redish, I am not even sure as it could be the light, when another cory comes close to this one the gills also look a bit more redish, but when it moves out they are fine.
Temperature is about 26. I only test kH and gH in my shrimp tank, with this one I don't test regularly and I don't have a master test kit.

I put some water to age a bit and will do the change in about an hour before I go out for the whole afternoon. I hope the guy will make it.
Oh, one last thing, I add Equilibrium to all my tanks. But the last water change was last Thu or Friday, so it doesn't seems to be something from the water or anything like that.
Total surprise as nothing is changed really.

[Mferko]

if you have any melafix on hand maybe add a little, hope he does ok

[InfraredDream]

I have Primafix
But don't want to medicate the whole 20 g tank
If it will help, I can take the guy out and medicate it.