Why do my corydoras die?

[GiantCheeseMonster]

80l tropical tank. Very well-established, lots of live plants, normal water parameters, good filtration. Not overstocked. I rarely have a death, but for some reason any corydoras I get die within a few months. They don’t look ill, I just find them dead. My other fish live for years. Are they a short-lived fish, or am I doing something wrong? I feed them cory pellets as well as flake food. Nothing in the tank to bully them.

Are they getting enough food? I only have a betta with my corys but I have to distract him to make sure the corys have enough time to gobble their food!

I think so, I feed them Cory pellets which the others don’t eat so there should be.

What kind of substrate do you have?

Sand.

What kind of corys are they? I've had rotten luck with my group of peppered corys - never lost one before this tank! Albinos are thriving, meanwhile. I was going to suggest other greedy fish might be nabbing their pellets but if there's only a betta in there that's unlikely.

There’s the Betta and a group of cardinal tetras - that’s it. Nothing to bother the corys. Interesting though, mine are the little speckled ones - not the peppered type, the ones that look like Dalmatian dogs. I wonder if I’d have more luck with a different type.

Our corys seem to do best with benign neglect, tbh. They much prefer us not to clean the bottom of the tank too much, and they prefer plants, moss balls and the slime that grows on decor to any commercial fish food. Though we do feed them, obviously! The same food as the tetras and the Betta.

One died a couple of years ago (the shrimp ate him!), but the other two are well into their fourth year.

@GiantCheeseMonster

There’s the Betta and a group of cardinal tetras - that’s it. Nothing to bother the corys. Interesting though, mine are the little speckled ones - not the peppered type, the ones that look like Dalmatian dogs. I wonder if I’d have more luck with a different type.

We have white ones. And we only feed once per day, in the morning.

Corys do best in groups of 6 as they need to shoal together to feel secure.
They are also soft water fish so unless you live in a soft water area you would need to use RO water.
I presume you change their water weekly and add seachem prime every water change. I love seachem prime it's fantastic stuff and goes a long way.
Have you tested your water perimeters recently to make sure your ammonia, ph & nitrite levels are correct?
I love corys and have looked after them for a number of years and they are very easy as long as you cover the basics.
Good luck.

Yes, I do all that It’s very soft water here, I keep them in a shoal, test the water weekly, treat it appropriately….as I said, my other fish do fine. Had the tank for three years and the Betta and tetras are the originals. It’s only the corys that die regularly which is why I’m baffled. I can’t think what’s going on.