Oxygen...?

No it's not! Drop the water level right away to get more splash from the filter return. Do a partial water change to reduce the organics dissolved in the water.

What can you tell us? Plants? CO2? Too many fish? What happened in the last week that's unusual?
 
Perhaps we should ask what most of your fish are? Gouramis and corydorus catfish (and their relatives)? If those or others with accessory respiratory functions, it is normal behavior.
 
Is this their regular behavior or a recent change in behavior?

Some fish, as mentioned by RTR, do sometimes surface breathe. Depending on the fish, this may or may not be normal behavior.

Gasping at the surface may also be a sign of gill distress caused by things like ammonia or nitrite poisoning. Have you tested your water chemistry? What are your levels?
 
my water levels are tested with hagen,
todays chemistry readings.

thanks for the info.
ph_______6.8
gh_______180
kh________70
no2_______0.3
no3_______50
nh3/nh4___0.0

And i have hagen co2.
 
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Both the NO2 and NO3 readings are a little high, I believe.

I know that NitrIte should not be detectable in a mature system, so, assuming that you are not supposed to be in the middle of a cycle, you need to do some water changes quickly.
 
I would suggest that nitrite toxicity is the primary culprit - since it interferes with oxygen transport in the blood.

Why do you have nitrites? New tank, new fish? antibiotic/other med use?
 
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