Neon tetras being weird

[egg7]

i just got these little guys 2 days ago. i had 5 but lost one. they are in a 5 gallon tank and at first they were swimming around and acting normally but now they are all sitting up at the top of the water just floating around. they will go and swim normally every once in a while but they always go bacm to the top. I also have a cory catfish in there too and it keeps on going to the top then quickly swimming back down. Does anyone know whats going on?

 

[Byron]

My first suggestion would be to do a significant water change now, at least half the tank volume but more up to 70% advisable. Us a conditioner, but nothing else.

This is clearly a problem respirating, but it could be any one of several things: lack of oxygen, ammonia, nitrite, pH shock, toxin in the water. More data on this tank will possibly help us narrow this down. How long has it been running, was it cycled.

What is the pH? And the GH? The white gravel substrate, do you know what it is composed of? White can sometimes be calcareous, dissolving mineral into the water, which would not help neon tetra (or cories).

Cories often go the the surface for a gulp of air, but this should not be too frequent; the more they do it, the more likely something is wrong in the water, same issues as above.

 

[NickAu]

That substrate is not suitable for Cories.

 

[Demeter32]

You need to change a good portion of that water fast. When fish gasp at the surface it is a sure sign of bad water. Do you know about the Nitrogen cycle? If not do some reading up on it. I would bet the tank was not cycled so the fish are suffering from high levels of ammonia and/or nitrite.

I agree completely with Byron and Nick but will also add that 5gals is far too small for corydoras and neons. A 20gal is the minimum for both and both should be in groups of 6+.

 

[King puff]

How strong is the filter? There seems to be a white bio film on the top. This should have been washed away by the filter.