Cardinal gasping

[Brandon3152134]

So 7 months ago I started cycling my 55 gallon salt water tank. That tank is doing great its only got 2 clowns and some soft coral in it. I have done freshwater for the past 4 years and have had a good amount of experience with quantine. I always qaurantine. So the problem is i got 3 fish yesterday and put them in 2 10 gallons that I cycled about a week before with filter media. I got a fire fish and 2 cardinals the firefish is not shy and is really cool but the cardinals aren't as well. One of them seems perfectly fine and swims around and eats but the other isn't swimming much and when he does its to take a gasp of air at the top the rest of the time he lays at the bottom and breaths heavily
There is a divider between them
Ammonia. Is 0
Nitrite 0
Nitrate is undetectable with my current test kit (under 1 Ppm)
So I don't know what the problem is and what can I do to fix it

 

[Flippers4pups]

If the fish isn't showing any signs of external parasites, it could be velvet.

 

[Humblefish]

Could be parasites or flukes inside the gills. A FW dip would at least confirm/rule out flukes: https://www.reef2reef.com/threads/freshwater-dip.248898/

 

[Brandon3152134]

No it has saltwater rich and Im treating it but would that cause this also I did not dip him should I do it now or wait till tomorrow

 

[Brandon3152134]

Well the other fish are all swimming and healthy but the cardinal Didn't make it

 

[Flippers4pups]

Sorry for your loss.

 

[Brandon3152134]

Its okay at least he didn't get my display tank sick

 

[Andrewalex11]

I agree with Humblefish, even some other issues that can arise medically are capable of not making things like mucus excrete from gills etc. I'd sit there for a good while and observe movements and other behavior that could help you determine a possible illness diagnosis. You shouldn't put a fish through the stress of certain medical treatments that are available for sea life unless you are as positive as you can be about diagnosis due to how absolutely stressful it could be on the animal.