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Discussion Starter · #1 · (Edited)
Hello,
a lot of my fish seem to be swimming at the surface. I did water quality check and Nitrite, Ammonia are at zero and nitrate is below 5ppm. Could this be caused by over saturation of co2? If so what should I do?
Run air pump? Do water Change? Thank you in advance for any advice.
Chris
 

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What 's the water temp? Do you have decent surface flow? If they're at the surface and gasping but you don't run CO2, the temp may be too high and has reduced O2 content or a lack of surface flow can cause an O2 issue too. Air stones actually do not ad any appreciable O2. They create flow at the surface which does.

Tommy
 
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Fish at the surface that are not normally there...
Fish gulping air or gulping the very top layer of water that do not normally do this...
Fish that do make periodic trips to gulp air/water at the surface that are doing this more often than normal or are hanging out at the surface...

Are all RED ALERT emergencies.
There is SOMETHING going on with the oxygen supply.

The first step is to add oxygen to the water. You can do this by improving the splashing at the surface. Add bubbler, a circulation pump or power head, raise filter outlet, or simply pick up some tank water in a cup and dump it back in, a lot. You can add oxygen in the form of hydrogen peroxide. An emergency 50% water change can drop the levels of ammonia or nitrite and raise oxygen levels, but may cause more problems if your source water needs more prep than just 'add dechlor'. If the water is OK, you can increase oxygen levels when you add the new water by allowing it to splash into the tank, and sheet across the surface where it will gain oxygen.
Do not waste time looking for the 'best solution', implement something FAST.

Next is to figure out what is going on:
High temperature = less oxygen
Poor water movement at the surface = less oxygen lower down in the tank. Surface water will get its oxygen from the air, but this does not move through the water well unless there is good water movement.
High ammonia (> .25ppm) will burn the fish gills, leading to breathing difficulties.
High nitrite (>1ppm) will cause methemoglobinemia, meaning the blood will not carry oxygen very well.
Parasites in the gills, or infection with fungi or bacteria can lead to breathing difficulties.

Once you have figured out the origins of the problem you can take time to go find that power head that is buried in a box, or go shopping and get the medication if the fish are sick, do a larger, more complete water change, vacuuming debris and cleaning the filter.
 

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Discussion Starter · #7 ·
so after doing some reading I find that at night plants absorb oxygen from the water. In a heavily planted tank this can be bad for the fish as oxygen supplies are depleted. This would explain why the fish were fine at night and gasping in the morning. I thought that my filter return was disturbing the surface enough to allow oxygen to get in. I must have been wrong. I put a bubbler in the tank with a pump to get some more surface movement and within a half hour the fish were okay. I have now hooked the air pump to come on when the lights go off. I will update tomorrow to see if this is enough to keep the fish happy.
Thanks for the answers plant people.
Chris
 

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Looks like you have put most of the pieces of the puzzle together.

As bigbadjon hinted at, when the lights are off at night, the plants aren't photosynthesizing so the co2 is not being used up, so if you are still injecting co2 at night, the co2 concentration can/will build up. And as you already learned, plants also use oxygen at night when the lights are off, hence the reason some use air stones at night (add more oxygen and off gas co2 if it's constantly being injected at night), when their normal surface agitation is not enough (surface agitation is limited to minimize off gassing co2, but it does make it a fine line).

While plants photosynthesize while the lights are on, they use up the co2 and give off oxygen (o2), which is why the fish are okay when the lights are on.

I've previously gone more into depth on how co2 kills fish, for anyone interested, you can read about it here.
http://www.plantedtank.net/forums/8...-fish-build-up-tolerance-co2.html#post8806105
In short, co2 does not displace o2 levels (and vice versa), the water can have high levels of dissolved oxygen and the fish can still die from too high levels of dissolved co2.

Diana covered most of the other possible reasons for fish gasping at the water surface.
 
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