Cory hiding, acting strange

[outofwater]

I have 5 cories in my 29g. 2 albino (male and female), 1 bronze female, and 2 peppered males.
A couple of days ago I noticed the male albino was acting funny, or so I thought when I saw him head deep into my sword plant. Yesterday I noticed he was laying on a plant kind of sideways, I tapped the glass and he moved out to the sand. Earlier this morning I saw him upside down on a plant and when I tapped the glass he went into a frenzy and swttled behind a rock.
i had to go out, upon returning home i see him now basically buried himself, sideways, between the rock and the glass. All the other cories are acting normally, the other fish as well (13 neons and 3 ottos)

Only recent change to tank is adding a strand of hornworth to it. I just tested the water, pH is about 6.5, as it always is, 0 ammonia, 0 nitrite, about 5 nitrate.

Tank is moderately planted, always kept at 77°, and here is a picture of it I took just now, and one of him in this "hiding spot".

Thinking of taking that cory out to a small 5g tank to quarantine him, but unsure if that will stress him even more, and I can't see any obvious signs of disease or it being hurt so I don't think there's anything really to do but to keep waiting it out.

Any feedback is greatly appreciated.

 

[Lcc86]

Have you had your cories a long time? It may be that if there's no other obvious illness among the others that this one may be coming to the end of his life. Are there any obvious signs of injury? I tend to agree that it might be more stressful to move him. Hopefully someone can give some ideas.

 

[outofwater]

Well, he just passed. I noticed he was breathing fast behind the rock.
I've had the tank and those fish for 2 years now.

Took the little guy and buried him in one of my house plants. Circle of life.

Feel bad as the cory gang is now only 4. On one hand I want to get more so their group stays at least at 6, on the other hand they're all mixed types and either I get more of just one type, or replace them all as they age with just pygmies or pandas, which recently really picked my interest.

Rest in peace little guy, you'll be missed.

 

[outofwater]

Adding pics. I didn't see anything abnormal, although those dark spots inside the gills intrigued me. Was thinking of opening up the little guy to check the gills better, but didnt have the heart. Maybe more experienced peers here can point something so I ensure the rest of my tank stays healthy, this weekend is water change, I'll do the usual 15% I do weekly.

 

[Lcc86]

Sorry he's passed sometimes these things can just happen, maybe it was his time. Perhaps do a precautionary water change and keep a close eye on the test for the time being.

 

[MaloK]

Please, refrain from tapping your aquarium glasses... As ridiculous at it seems, It can be very stressful for some fishes.

Others will have a positive response and come to see you, but if it startles them, don't do it.