Cardinals Dying!

[Mark_b]

I have had some cardinals in my tank for about 2 weeks and over the last 5 days about 4 have died overnight. I have noticed today that about 3 more seem to have distended bellies, also possibly a slight loss of colour in the red area above the belly, their behaviour seems normal.

Could these be about to die too?

Currently the water conditions are fine, ie nitrites nil, nitrates nil (heavily planted tank), ammonia nil, ph 7.4, temp 26 C. I have four silver dollars which had whitespot 4 days ago. I am doing a five day course of treatment with Myaxcin(or something like that),the whitespot has now gone and i have just one day more of treatment to go. Every other fish now seems fine except the cardinals. The tank is 120 US gallons, planted, there were 20 cardinals and now about 16,5 ottos,4 amano shrimp,4 silver dollars, a common pleco and ten danios. 1 danio does seem to have quite a dark head but i could be imagining that.

Any ideas guys?

Is it possible that they are starving because the silver dollars and the danios are far more active at feeding time and tend to gobble up most of the food before the cardinals get into the action?

P.s. The tank is well cycled.

[wetmanNY]

Small fish are more susceptible to medications that larger fish. And tetras are susceptible to some medications.

[Mark_b]

I thought that it could be the medication thats why i mentioned it. Do you think that the cardinals with the swollen bellies could be done for or do you think that if they survive till after the treatment that they will recover?
Anyone else agree that it could be the medication?or any other possiblities?

[Dean]

If you have a heavily planted tank during the day plants produce oxygen but at night they produce co2. So your cardinals my be sufocating(sp.) during the night.

[tanker]

I think it is the medication too. Cardinal (tetras in general) are very picky to medication. Also your PH is kind-of-high for tetras. Should be about 6.8 If you can get PH a little lower it may help.

[Mark_b]

Thanks for the replies everyone. I think it must have been the med because since i stopped the treatment they have been looking a lot better.
cheers