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CO2 loading on the surface of water

> From: Ivanstein at webtv_net (Ivan Trail)
> Subject: CO2 loading on the surface of water
> In light of the recent discussion of the CO2 levels on the surface of
> the water in a tightly closed tank, I would like to share my theory, of
> which I have put much thought into.
> One question first:  Why would anyone put a tightly sealed cover over
> their tank?  I personally have never seen a pond or lake in the wild
> covered in this manner.  Maybe there is a reason I don't know of.  If so
> please tell me.

First a clarification: Anabantoids indeed breeth atmosphefic air with 
the labyrinth organ. They have gills too but are unable to get all 
the oxygen they need with them. If an anbantoid is prevented from 
breething at the water surface it will drown. I had a female betta 
drown on me recently after it got stuck in the drainage hole of a 
flower pot. 

The cover should not be airtight. But it should be tightly fitting 
for anabantoids to ensure that the air is the same temperature as 
water. Otherwise, anabantoids are prone to catch cold. In our cold 
climate, room air temp is usually several  degrees below the temp we 
keep in our fish tanks. 

> Now, back to my theory.  The law of partial pressures states in a
> nutshell, "The gasses in a given container will be evenly distributed
> through out."  This is why there is no cloud around a smoker.  The smoke
> seeks to make a balance with all other gasses in the room.   No fog
> around your face on a cold day.  No green cloud of foul aromatic esthers
> aruond a person who has just eaten Uncle Bob's Flamin Hot Chili.
> We know that in a tank with fish, enough O2 exists to support the life
> of the fish.  The evidence is obvious.
> So, if the CO2 dissipates out of the water, then so should the O2 and
> whatever other gasses are present in the water.  thus the layer above
> the water in a tightly covered tank should be made upof the same gasses
> in the same proportions as in the water, all equaly mixed.

I am not a physicist, but I do know for fact that CO2 is heavier that 
'normal air.' With a tightly fitting cover, there will be very little 
air movement between the water surface and the cover. Hence, the 
gases may not necessarily be evenly mixed. I think it is quite 
plausible that there will be a layer of CO2 rich air immediately on 
the water surface whereas O2 will rise higher. 

> now that only leaves to assume that since the gasses in the water are
> able to support life, then the accumulated gasses will support life
> also.
> Just the thoughts from my humble brain.
> Ivan