o2 vs co2

[steelhealr]

Hi Nutcase..don't worry....I don't come here to blow big words out and confuse people.My second specialty is Undersea and Hyperbaric Medicine. I never want to confuse anyone here...but..it sometimes helps people to understand how their aquarium is impacted by stuff we all learned years(?) ago in science. No gas law is perfect for scientists except in ideal situations....but most work really well for our purposes to understand what happens in an everyday kinda way. To try and help you and summarize here:

1) most things around us will tend to reach an equilibrium as far as gases go
2) I don't think opening the tank hood to 'get fresh' air does anything unless you had, for some reason, a tight tank hood
3) There is no way to artificially increase the oxygen in your tank per se, short of bubbling 100% oxygen thru it. You can help maintain Bignose's equilibrium discussion by maintaining adequate surface area of the tank to open air so that the ambient oxygen (O2 in the air) can readily diffuse into it. Airstones improve it by circulating bottom water(lower O2) up to the top of the tank; filters improve it by increasing the amount of water exposed to air and by agitation
4) CO2 diffusers assist plant growth by providing the substrate necessary during photosynthesis to make 'sugar' during the day. Plants revert to respiration at night, taking in O2 and giving off CO2..hence....stopping the CO2.

Whew..I think I'm done with this. SH

 

[nc_nutcase]

What about the tanks with glass lids that sit a 1/2 from the surface... fresh air has got to do it some good.... lol...

I'm glad the discussion got deep. I didn't understand some of it but it was a good introduction (or maybe reintroduction) to the concepts.

Thanks,
Toby

 

[silvershark]

umm yeah, sure

now can i really upset everyone and just ask one more thing which, i'm sure, has been answered in non "dropped out of school" lingo?

do plants release enough co2 at night to compensate the amout they absorb during the day?!?!

i'm so sorry guys! just a bit confused and didn't expect all the proper answers in that format!! i'm gonna have to print this out and get down the library!!

 

[Undawada]

do plants release enough co2 at night to compensate the amout they absorb during the day?!?!

Plants will respirate (breathe), and absorb CO2 and release O2. This process is reversed at night, but not as much transfer takes place, having a net decrease in CO2 and increase in O2. The overall effect of live plants respirating is more O2 for your fish.

Of course this depends on how long you leave your lights off, how much CO2 / O2 is available... but I don't think anyone has ever had a fish die from plants absorbing too much O2 at night, if that's your worry.

Fish respirate (breath) and absorb O2 and release CO2. My understanding is that CO2 is relatively hard to dissolve in water, and fish alone don't produce enough CO2 to maximize your plant's respiration. If you stocked enough fish to supply CO2 to your plants, you would be massively overstocked. This is why some people use supplemental CO2.

The more CO2 is available for the plants, the more they respirate and more O2 is released into the water. So with a planted aquarium, adding Co2 helps both your plants and the fish, by forcing the plants to respirate more O2. That being said, water can only dissolve so much gas of any type before it becomes saturated, so if you add TOO MUCH CO2, you may not be able to absorb any more oxygen, which will cause your fish to stop respirating and die.

[disclaimer : This is from my own experience and understanding, some of the above may be wrong ]

 

[Undawada]

To understand surface agitation and equilibrium, I am reminided of an experiment that I did in science class.

Take a paper plate and draw a line in the middle, cutting it in half.

On one half, draw blue lines so it looks like water. The other side will be the air.

On the "air" half of the plate put a handful of yellow beads (this will be Oxygen).

On the "water" half of the plante put green beads (this will be Carbon Dioxide)

If you hold the plate still, some beads may roll around, but more or less the concentration of yellow will still be in the air, and green will still be in the water.

If you shake the plate gently, the beads will scatter and mix, and before long you have roughly the same amount of green and yellow in the water.

This is equilibrium.

 

[silvershark]

cheers undawada! i understand it now! so you cant over do the o2 but can over do the co2!

thanks everyone!

 

[Bignose]

And you can take undawada's example a little farther. After a certain amount of shaking, further shaking doesn't do any good right? At this point, we can say that equilibrium has been reached. Well, if you started taking off yellow beads on just one side, this represents the sink of oxygen to the fish. So, there is now a void, or the system is not in equilibrium. Further mixing and shaking restores the equilibrium. Similarly, the CO2 injector adds green beads, and again it takes time to shake to bring the system back to well-mixed equilibrium. But, you'll notice the system always heads toward mixing back up again -- heads toward equilibrium. (in fact, for those so inclined, this is actually one part of the the laws of thermodynamics)

Equilibrium is simply the point at which the state of the system (that is the concentrations of the gases, the temperature, etc.) will not change given more time. It is also known as steady state.