40 Gallon Tank Oscar heavy breathing and not eating in new tank

Help! I upgraded my Oscars tank from a 20gal to a 37gal since the last one sprung a leak and she was getting to big for it any way. Since I have moved her into the new tank about 2 weeks ago she has NOT been herself. She doesn’t eat and she doesn’t swim around very much either. She looks as if she is gasping for breath but I have a filter running and I also added and extra air line in there. There is a goldfish (one she kept as a friend for months now and has gotten to big to eat) in there with her and he is acting perfectly fine!

I’m not sure what to do and this is worrying me. I am no expert at all on gosh and tanks so please be nice.

Tank
What is the water volume of the tank?
How long has the tank been running?
3weeks
Does it have a filter?
Yes
Does it have a heater?
No- I have it tho
What is the water temperature?
What is the entire stocking of this tank? (Please list all fish and inverts.)
Goldfish and the bare minimum decorations since she will tear apart anything I put in there.

Maintenance
How often do you change the water?
Monthly/every other month
How much of the water do you change?
As much needed to clean the tank
What do you use to treat your water?
Stress cost..
Do you vacuum the substrate or just the water?
Both

*Parameters - Very Important
Did you cycle your tank before adding fish?
Not sure what this means
What do you use to test the water?
Yes
What are your parameters? We need to know the exact numbers, not just “fine” or “safe”.
Ammonia: my tester doesn’t have this
Nitrite: .5
Nitrate: 40
pH: 6.5

Feeding
How often do you feed your fish?
Once daily
How much do you feed your fish?
a few mini shrimps or pellets each

What brand of food do you feed your fish?
Various
Do you feed frozen or freeze-dried foods?
Dried

Illness & Symptoms
Illness & Symptoms
How long have you had this fish?
Since dec 2020 (got as baby)
How long ago did you first notice these symptoms?
2 days after being in new tank
In a few words, can you explain the symptoms?
Have you started any treatment for the illness?
Was your fish physically ill or injured upon purchase?
How has its behavior and appearance changed, if at all?

This is the tank I got and the filter it comes with

 

Welcome to fishlore.

it sounds like there are a few issues here - depending on where you are in the world your oscar will need a heater. Secondly, it sounds like the tank isnt cycled based on the nitrite reading. You therefore dont have any beneficial bacteria in the tank to break down the waste being produced by your fish, so it will be slowly poisoned by ammonia and nitrites. Did you move the filter or any of the media from the old tank? It also sounds like you arent changing much water, which wont be doing any good either in a tank containing such messy fish.

it will also need a much bigger tank than the one you have now too. Maybe not right now, but soon.

 

Welcome to fishlore.

it sounds like there are a few issues here - depending on where you are in the world your oscar will need a heater. Secondly, it sounds like the tank isnt cycled based on the nitrite reading. You therefore dont have any beneficial bacteria in the tank to break down the waste being produced by your fish, so it will be slowly poisoned by ammonia and nitrites. Did you move the filter or any of the media from the old tank? It also sounds like you arent changing much water, which wont be doing any good either in a tank containing such messy fish.

it will also need a much bigger tank than the one you have now too. Maybe not right now, but soon.

I live in Phoenix, Arizona but I’ll definitely get the heater set up. She was doing just fine without one this whole time tho so I’m not sure that’s it. How do I fix the cyling issues ?

 

I live in Phoenix, Arizona but I’ll definitely get the heater set up. She was doing just fine without one this whole time tho so I’m not sure that’s it. How do I fix the cyling issues ?

They need it around 75-80f, but then your goldfish may not be happy with that either. It may not be that but it could be a contributing factor.

you’re basically doing a fish-in cycle now. Have a read of this article which gives an overview of what the nitrogen cycle is and the various stages of it. You definitely need to get a test kit which measures ammonia - most use the api freshwater master kit.

Aquarium Nitrogen Cycle

any questions, just ask. Plenty of people on here to help out.

 

The fact that you have nitrites is not a good sign, and you should definitely get the cycle sorted out as recommended. It is possible though that it could be stress related. My male Cichlasoma reacted something like this when I moved him to a different tank, he sulked and hid behind a log and would not come for food, I can’t remember for how long exactly but it was quite a long time, he gradually became more confident though.