A New Way of Supplying CO2 - the LUWAT


Lifetime Charter Member
Lifetime Member
Jan 24, 2005
Today while running I mused about useful tools that we might have available in 5 years - the $50 CO2 meter; the photon meter, which would count the number of photons that were striking a surface, and the psuedo-photon generator, which would generate particles that would excite plants the way that photons from light do. These three would revolutionize the maintenance of aquarium plants.

But they are in the future. There is another device that could be in use today that would simplify and make less expensive the providing of extra CO2 to planted aquariums. That is the homemade lung-to-water CO2 transferer. (LUWAT).

To make a LUWAT one would need only an inflatable container to hold the CO2, a four legged table of apprporiate size, a flexible plastic tube to transport the CO2 to where it was needed, and a bar bell disc. Reasonably healthy lungs would also be needed.

To use the LUWAT, one would first fill the inflatable container (a balloon or beach ball, for example, or maybe even a trash bag) with exhaled breath that contains CO2. Then the table would be inverted and the inflatable placed between its four legs, to prevent it from moving. The disc would be placed on top of the inflatable, to force the CO2 through the tube to the aquarium. And that's it!

There are a number of engineering question to be answered. For example, how large an inflatable would be needed to hold a several day supply of CO2? What size table would be needed? How heavy a bar bell disc would be needed? The inflatable in the table frame would be approximately rectangular. Would a cone-shaped frame be better?

The advantages of this would be its simplicity, its low cost, the opportunity for lung exercise, and its obvious environmental benefits - less CO2 being expelled into the atmosphere (although some might see that as a drawback, too.)

I would be interested in seeing how folks do with this.


Tom Barr

Staff member
Jan 23, 2005
Paul Kromboltz made a similar idea years ago with breathing in a bag, then add an air pump to pump the exhaled CO2 back into the tank.

See APD archives.

Our lungs only exhale maybe 50%, birds can exhale about 90%, they have far more efficient lungs than we do.

Tom Barr


Plant Guru Team
Lifetime Member
Sep 23, 2007
South Florida
So now we need to get BIRDS to fill the bags for us????? Will any bird do?

I suppose now I need to understand how to care for them as well?

This hobby is getting way too complex LOL

That is interesting though about their lungs. It makes sense but I did not know they were that much better functioning than our own....


Lifetime Charter Member
Lifetime Member
Jan 24, 2005
Sacramento, CA
I found, while experimenting with drop checkers, that you can build up a pretty good supply of CO2 in a small amount of water, using a straw and blowing into the water. But, for even a 10 gallon tank, I think you would pass out from hyperventilating before building up as much as 10 ppm.