Why are my cardinals dying?

[sharkbait]

Newish tank: though with water and gravel from old tank, guppies assorted tetras, swordfish dwarf Gourami.

Everyone else seems fine, apart from a bit of ich. but I have had five cardinals snuff it over the last three weeks.
They do seem rather shy and reluctant to come up to feed. whilst everyone else, (notably the greedy guppies) gets the food. Am I starving them. I dont like to fill the bottom with unused fish food so I have been feeding the fish a little and often. Should I put more in less frequently?
Or are they a more difficult species to keep.
PS Most of them died before the ich treatment, so I don't think its that.

 

[Alien Anna]

Cardinals are fine in a well matured tank with good water quality, but if you have the slightest problem, they will die pretty quickly

First thing to do, test your water for ammonia, nitrite, nitrate and pH. Regardless of the results, do a 20% water change immediately and a 10-15% water change every day if you have something worrying in the results.

Any ammonia or nitrite in your water is a major problem, especially with cardinals so if you aren't familiar with cycling a tank, please follow the link in my sig for my article that hopefully explains it, and will give you some emergency steps to take if your tank is not cycled.

Cardinals are sensitive to nitrate, so if nitrate is higher than 25-50 ppm, you should regard that as a problem. Water changes and plants are a good way to get it down, but do test your tap water as many countries do not have "safe" limits on nitrates in tap water. If that is the problem, get back to us for advice.

Cardinals are very sensitive to pH swings. If the LFS pH is different to your own, acclimatise them gradually. If your pH has suddenly risen or dropped also get back to us and we'll try to help you figure out why.

Another point is that cardinals are wild-caught, not bred in captivity, and since a 6 year old cardinal looks practically identical to a 2 month old cardinal, its pretty well impossible to know how old they are. Some of the cardinals may be elderly and therefore less able to cope with capture and acclimatisation to different water conditions, but there is sadly nothing you can do about that.