CO2 Dispersal From An Aquarium

Probably a stupid question, but what happens to the CO2 that finds it’s way up to the surface of an aquarium. I believe that CO2 is heavier than air so technically a layer of the gas could form just above the surface of the water. It obviously doesn’t or the fish would suffocate. Presumably it’s dispersed by air currents etc.

Gaseous dispersal is one of the scientific explanations for having a siesta period. The molecular weight slightly influences the speed at which a gas can disperse. And in water this is slower than in air (due to the relative weights of the solvent (ie water is heavier than an oxygen / nitrogen mix). Aquatic plants produce oxygen / co2 faster than these gases can naturally disperse in water. It is suggested that after about 4hrs, the layer of oxygen surrounding an aquatic plant's leaves is sufficient to (at least partially) block the plant's access to the CO2 in the water. So by turning the lights out for a couple of hours, the plants start to respire and use up the o2, replacing it with co2, which they then use when the lights come back on.

Obviously the water flow around the leaves makes a difference to the dispersal rate and therefore the optimum photo periods.

And each plant type has different requirements and production rates too.