Pictus Catfish sick??

[Taylorxc]

1~ The fish in question is a pictus catfish, and he has been swimming straight up to the top of the tank then sinking back to the bottom and sometimes laying on its side

2~ [i just did a test strip and the nitrate and nitrite are both in the danger zone so I will start doing a water change right away but I don't see why it wouldn't affect the other fish and why they aren't acting weird]

3~ the tank is a 55 gallon and has been set up for 2 weeks but they used to be in a 30 gallon for many months
4~ I'm using a fluval 306 for filtering
5~I have 5 goldfish, 2 pictus catfish, and then a tiny pleco. Two of the goldfish are about 3 inches 2 of them are about 2 inches and then 1 is about an inch. The sick catfish is 2 inches while the second is 3 inches and the pleco is an inch

6~ I haven't performed a water change yet

7~ I've had the catfish for months, while acclimating them to this new tank I had them in their old water and added about 2 cups of water every 15 minutes for about 3 hours

8~ All of the plants are new but we're put in at least a week ago

9~ I feed them National Geographic tropical flakes and tetra pro Cory wafers

As I'm typing this he is laying on the gravel but his gills are still moving, any help would be greatly appreciated asap thank you very much!! And if you have any other specific questions please do ask

 

[King Fisher]

You need to do a 25-35% water change asap if your nitrites and nitrates are high. You might have not completed your cycle before you added your fish. It's not uncommon for some fish to show signs of bad health while others don't in less than ideal water conditions. At this point you should just do a water change. Probably another one 6-8 hours after. Also it isn't good to mix a pictus cat with goldfish. Pictus is a tropical fish. You could get away with the lower water temp with the pleco but not the cat.