Solubility of Gases in Your Aquarium
N 2    O 2    CO 2   NH 3

For simplicity forget the units, just consider them as a relative amount or ratio.

Nitrogen               N 2     0.0164    1  

Oxygen                 O 2     0.0317     2

Carbon Dioxide  CO 2    0.878     54

Ammonia             NH 3      710     43300

Your aquarium has a complex equilibrium of nitrogen, oxygen, carbon dioxide and ammonia. Concentration is temperature dependent but there isn’t any significant change in temperature.

Nitrogen is 4/5 of the air we breathe and the least soluble, the least harmful. You may not realize it but you can suffocate fish when you fill your tank with microbubbles for several hours. Nitrogen saturation occurs when nitrogen displaces oxygen because of the scheer number of bubbles and their size. Large bubbles quickly rise and burst.  Micro-bubbles can take several minutes to rise to the surface while adding more nitrogen than oxygen.

Oxygen vs Carbon dioxide  Oxygen O 2 isn’t very soluble compared to carbon dioxide CO 2  but carbon dioxide  concentration  in the atmosphere is 400 ppm. (<0.01%) The fish’s respiration produces much more CO 2 .  It’s not the increase in CO 2 that suffocates fish it’s the lack of O 2 .  Most CO 2 is removed by photosynthesis in the aquarium,  surface agitation, water falling through overflows and sumps and protein skimmers while adding O the same time.  Carbon dioxide in the room isn’t lowering your pH, as internet wants you believe, it’s what is produced IN your tank.  Your salt mix cannot stabilize the pH.  I never have such changes using Crystal Sea.

Ammonia never is a gas in aquariums because of super solubility and extremely harmful. The major source of NH 3 is fish waste. When ammonia and water mix they form ammonium hydroxide (NH4OH).

Ammonium NH 4 + is what bacteria convert to nitrite. When a tank starts, ammonia NH 3 builds up. A small amount becomes ammonium NH 4 +  that initiates bacterial growth. When the ammonia NH 3  is consumed a small amount of ammonium NH 4 + remains. This is why test kits always show 0.25 ammonia NH 3  when it actually is ammonium NH 4+ and harmless.

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