Help Cory Internal Bleeding ?

My Albino Cory Die with an internal Bleeding ?
Anyone know how to prevent this or what to do ? I scared all of them might be die

Ammonia : 0 ppm
nitrite : 0 ppm
nitrate : 6 ppm
Ph : 6.5
I feed them Rubin Tetra Flakes

Edit : All Of my Albino are currently fine, No Red Gills, Swimming Actively to scavenge.
I found this one floating just now. Not moving at all so try to poke him/her, no respond at all.

I post some Other Corys pict To be sure that they're fine, any Help & Advise will really Help me a lot!
First timekeeping Corys. I dont want to mess it up

Looks like bruising... wondering if he spooked and swam super hard into something, or if maybe something in the tank fell on him...

Tankmates ars just juvenile congo tetras, correct?

NCaquatics said:

Looks like bruising... wondering if he spooked and swam super hard into something, or if maybe something in the tank fell on him...

Tankmates ars just juvenile congo tetras, correct?

Click to expand...

Yes, i remove some of the Indian Almond Leaf at the moment. To observe how they doing,
I didn't add anything to the tank