Losing my adult badis, but not the fry?

[Zoe]

So at the most I probably had about 6-8 adult scarlet badis in my tank (mostly females, 2 or 3 were males). At this time I seem to have only 2, and one of them is looking shabby. He looks a bit bloated, but is eating/swimming. The other seems fine, he's the male, although he seems a bit blah sometimes, not as showy, but I might just be reading too much into it.

I don't know if I lost them all slowly or if they all died very recently. My tank is heavily planted with lots of shrimp so corpses disappear quickly.

BUT, everyone else is fine and doing great, including the dozen or so fry in the tank, the oto cats, sparkling gourami and rasboras. And shrimp.

Nothing is big enough to eat or attack them.

Water parameters are fine. I do small water changes about daily and a bigger change every 1-2 weeks. The only recent changes were:
- I cleaned the filter (just rinsed the media in aquarium water)
- I got a new bottle of water conditioner
- I added a little bag (made of a piece of nylon tights) of crushed eggshells to the filter because my snails were looking shabby

Is it possible that the adults are just getting old and dying off? The badis have always seemed quite hardy and I wouldn't peg the adults are harbingers of doom if something was off. I got them about a year ago and they were adult sized.  I have read 3-6 years lifespan but I have no idea if that is accurate or just a best guess that has been perpetuated.

My other concern is diet. They eat mostly microworms and I am not sure what else they eat. I am sure they eat shrimp nauplii, and possibly the small snails I crush against the small and the frozen things I feed the tank.  Malnutrition did cross my mind but then why would they have thrived for so long? And between all those things I feed, surely their bases are more or less covered.

There may not be any answer here but no harm in asking!