Why not diffuse Air?

[Hebily]

When you use pressurized CO2, why not just diffuse air from an air pump into the water? All you would need is an air pump, a hose, and a diffuser/reactor/canister inlet... none of the worries of pure CO2. I'm just wondering why this is not done.

[Riiz]

Because the added surface agitation would de-gas whatever CO2 you're trying to introduce into the water.

[Hebily]

I'm talking diffusion, though... just as you diffuse CO2, so that the gas is absorbed in the water, not in bubble form.

[jpappy789]

You mean diffusing atmospheric air into an aquarium?

[Hebily]

yes, in order to reach higher than eq levels of both CO2 and O2

[bigwave]

From Wikipedia entry on "Carbon Dioxide"


Carbon dioxide content in fresh air (averaged between sea-level and 10 hPa level, i.e. about 30 km altitude) varies between 0.036% (360 ppm) and 0.039% (390 ppm), depending on the location.

So I would need to increase from 1 bubble per seond to about 2700 bubbles per second to get the same ammount of CO2 into the tank. I tend to think I would have a hard time getting that diffused very well. ;-)

[jpappy789]

Exactly.

[jpappy789]

Thought this was interesting.

Apparently if you were to supersaturate both O2 and N2 (which are both more abundant than Co2 in the atmosphere) fish would likely die.

http://books.google.com/books?id=wYtpGEbAB1cC&pg=PA78&lpg=PA78&dq=fish+nitrogen+gas&source=bl&ots=e90T6cFoup&sig=tR3IGsjkeWACqPYpSNoYOg16qHo&hl=en&ei=fiaLSt_VL5D0NaeRgLsP&sa=X&oi=book_result&ct=result&resnum=3#v=onepage&q=fish%20nitrogen%20gas&f=false

Not sure how accurate that is but interesting nonetheless.

[Star_Rider]

you can introduce CO2 by simply using an airstone.. it's just the levels in air are very low. you would only be adding what air holds.

by using CO2 you are upping the ante and can pump in a higher concentration.

[timwag2001]

Thought this was interesting.

Apparently if you were to supersaturate both O2 and N2 (which are both more abundant than Co2 in the atmosphere) fish would likely die.

http://books.google.com/books?id=wYtpGEbAB1cC&pg=PA78&lpg=PA78&dq=fish+nitrogen+gas&source=bl&ots=e90T6cFoup&sig=tR3IGsjkeWACqPYpSNoYOg16qHo&hl=en&ei=fiaLSt_VL5D0NaeRgLsP&sa=X&oi=book_result&ct=result&resnum=3#v=onepage&q=fish%20nitrogen%20gas&f=false

Not sure how accurate that is but interesting nonetheless.

Dont know much about it but wouldn't supersaturation of co2 cause the same effect as what that article suggests?

i was thinking of using another reactor just adding air into it in conjunction with my pressurized co2 system. just to ensure plenty of oxygen in the tank without any risk of co2 levels getting too high. just as an experiment to see what happens

don't plants use oxygen after their photoperiod and do most of their growing then too? so wouldn't saturating the tank with air feed the plants more?
if higher co2 levels are better for plants why wouldnt higher oxygen be better too?

[Canuck]

To elaborate on Star Rider's comments.

Diffusing air into an aquarium will (depending on temperature, altitude, etc) result in approximately 3ppm of CO2 and 5 to 8 ppm of O2. Pumping air through faster would only result in the water reaching this equilibrium faster. We attempt to reduce surface agitation in CO2 supplemented tanks in order to slow the outflow of excess CO2 in the water. And essentially adding an air diffuser is just adding more surface area (and a turbulent one).

In a "high tech" tank (with plants normally pearling) your O2 is quite likely already above normal equilibrium levels. Running air through a second diffuser will only reduce CO2 and O2 levels as the excess gasses bleed into the air you're diffusing through them. The level of gasses in water are always going to move towards being equal to that in the atmosphere.

Running an air pump at night is easier on the fish not because it increases O2 (which in most cases its probably reducing it in a planted tank) but because it reduces the level of CO2 in the water. The amount of O2 and CO2 in the water (within reason) is not as important as the ratio of the two.

[timwag2001]

but wouldnt o2 going into the reactor raise o2 in the tank? and i thought that i read that co2 doesnt displace o2. so why would it cause my water to offgas co2?

and wouldnt more o2 at night be better for plants?

[Canuck]

but wouldnt o2 going into the reactor raise o2 in the tank?

Not if the level in the tank is higher then that in the air (I assume we are not discussing pumping pure O2 into the water). The gasses move to where the concentration is lower. Think of it this way, instead of using a diffuser just increase surface turbulence, in both cases your increasing the amount of air, water mixture.


and i thought that i read that co2 doesnt displace o2. so why would it cause my water to offgas co2?

Your right but extra O2 isn't causing it to offgas. The answer remains the same as your first question. The CO2 is moving to the air where the concentration is lower. Think of it just like osmosis.


and wouldnt more o2 at night be better for plants?

Plants need O2 at night, you are correct but plants are net producers of O2 meaning they produce more O2 then they consume. This is why high growth heavily planted tanks have higher O2 levels then then any other type of tanks (at all points of the day). People run into problems because they're CO2 levels are so high compared to O2 levels that the fish can't rid they're bodies of the CO2 in their blood. (Osmosis again).

Curious piece of natural history. Did you know, the first major extinction event was caused by all the extra O2 that plants (algae) pumped into the environment.

[timwag2001]

gotcha
gotcha
gotcha

very interesting fact. never heard that before.

thanks

[Canuck]

Sorry, I'm not as eloquent as many of the other posters. ;)

[Hebily]

Jpappy definately brought up a very good point! Diffusing high concentrations of atm air into an aquarium would in fact give your fish 'the bends'. I can't believe I didn't think about the N2 Problem...

Actually, thinking about it more... the N2 bubbles shouldn't form unless the fish experience a reduction in water pressure. [N2] in the blood would be higher, but in solution, and in eq - This shouldn't be a problem. The reason it's a problem with divers isn't the higher [N2] in the blood, it's the N2 bubbles that form on rapid decompression. W/o decompression, the bubbles shouldn't form...

[Star_Rider]

good post to elaborate canuck..well said.

hebily, n2 as a gas forms bubbles just as other gasses. bends are cause by too rapid of an ascent where the gas expands too fast to escape and are trapped in the blood vessels or you exceed your total bottom time... remember that at 33 ' you are at 1 atm and gasses compress by half the volume for every 33 ' you descend.

bottom time for divers is based on how fast the body absorbs these gasses over a priod of time..too long and you will need a decomp stop to allow the gas to escape in essence.. too long bottom time and you have absorbed too much gas.

the reverse happens when you ascend..the gas doubles in volume every 33' you ascend.. the idea is to ascend slow enough to allow most of the N2 to escape the blood stream(diffuse)
in a nutshell anyway. ;)

btw if you ever fish deep water and bring up a fish really fast you can see the effect on the fishes bladder.