Cardinal tetras getting extremely skinny

Feed more regularly in smaller doses for a few days. My tetras will only feed from midwater as well. No surface picking, no foraging the substrate.

Is there anything in the tank with them that could be taking food before they can get it? I had this same problem with some CPDs as they are shy fish and like to eat from the water column so it's hard to get food to them. I found my filter was blowing the food around a lot so I've been turning it off during feedings to give the fish a chance to get some and the fish are gaining their weight back. What do you feed? I give mine mostly NLS community pellets (small .5 mm size as they are nano fish) and I soak them in a bit of tank water so that they fall when I put them in and the fish eat them as they fall. Barring that it could be some sort of internal parasite but let's hope not, try turning off the filters and getting food down to them.

might be some sort of parasite, if they're eating but getting skinny anyways. if you've actually seen them eat, then i'd maybe try a dewormer.

Treat for intestinal parasites. You'll have to determine if it's worms or protozoans.

Since theyre eating, you could try the deworming flake from angelsplus which contains fenbendazol.

+1 on the deworming food.

It could also be fish TB - hopefully not as that would really suck, but it's something to keep in mind if deworming them doesn't work.

Thank you. I feed a variety of blood worms or dried brine shrimp. They all ate tonight. I will try the dewormer food and hopefully that will help them.