One of my fish died :(

You should have used more hardy fish as your first fish after the fishless cycle. Then after that, you could've traded those back and gotten cardinals.

What's done is done.

Cardinal tetras are very sensitive. Depending on the source, the fish could've been weak, what have you. I don't know how big your tank is, but after you add fish in, you could get a spike in some of your readings as your bioload increases. I would take measurements again to see if everything is normal. If something is up, do a w/c.

At this point I wouldn't get any more. Wait and see, 'cause if one died more can/will follow. If you don't lose any more in the next 2 weeks or so, you can add more. Also, make sure you acclimitize them slowly.

Definately, more look better. But wait and see...

Also, you don't mention anything about your setup, planted, bare bottom, tank temperature, etc.

falcon

Are all the cardinals you got that skinny. Maybe it's just the pic angle, but he doesn't look so good, even ignoring the light spot. In general their bodies after their heads, should not be smaller or skinnier than their heads. It would mean they haven't been feeding very well, or possibly have internal parasites to explain the skinnyness.

I have not found cardinals that picky, as long as you get unstressed healthy stock, keep nitrates low, and acclimate slowly. I kept mine at a pH of 7.4, with minimal nitrates under 10 ppm.

--Mia

Mia, now that you mention it, the tummy does look flat. Something's wrong there. The belly should be nice and rounded. Did you get them like that? How are they feeding? If not feeding too well, give them a taste of bloodworms.

Have you done your water change after your cycle finished? The nitrate seems a bit high.

As for getting them to eat flake, just make it sink a bit near where they school. I've used the micropellets too, but they are almsot too small, and the fish don't notice them as well. Mine ate anything, you just had to get them to notice it.

--Mia

I assume you treat the water at w/c. Since it's a small tank, I would turn the filter down at feeding time. Also, make sure you don't overfeed. Cardinal tetras are not big, fast eaters and I would consider getting maybe 3 cories for the bottom to make sure the food is not rotting away at the bottom, contributing to your high nitrates.

High nitrates (5-10 ppm) are good only if you have high lights and lots of co2.

The nitrates are okay if they're down around 25, but if their up around 50 they can stress the fish out. Cardinals do not like nitrates.

As to food. You could turn off the filter if you wanted as long as you turn it back on. I dould just take a few whole flakes and dunk them underwater. They should sink, just do this somewhere the fish are likely to see it. If they see it, but don't go after it, try the bloodworms.

--Mia