they sometimes lose there color out of stress so it may well be normal
however they do need to be kept in groups of at least 5 so do all your other types of tetras, i would reccomend you take bake one type and get at least 2 more of each
i would also take back your danios as they need to be in groups of 5 or each type and doing that will seriously over stock your tank
Stocking suggestion
2 dwarf blue rainbow fish
2 schools of 8 tetras of the same breed
2 ottos
perhaps something like 4-5 corydoras
not trying to be nasty here but your fish wont be happy as it is
oh and here is some info on cardinals
http://www.aquahobby.com/gallery/e_C...n_axelrodi.php
http://www.tropicalfishdata.com/tetr...nal_tetra.html
http://elmersaquarium.com/10tetra_cardinal.htm
-olie