Oxygen in the water........

I am kinda confused on oxygen in the water. I have read here that the salt water fish "need all the oxygen they can get", but yet we strive to get the air bubbles out of the water system. How then does the water stay oxygenated enough to form the vital oxygen chain that will make the fish healthy?

Edited by Skyetone

Marcus wrote: Keep in mind that anything that photosynthesizes, takes in carbon dioxide and releases oxygen, when its photosynthesizing.  I believe that at night, its back wards.  But thats why you run a refugia light at night so that something (caulerpa and other algae) produce oxygen at night, thus keeping your pH up.

I do think Oxygen is very important, and often overlooked.  What is of importance is dissolved oxygen and not simply large bubbles.  Large bubbles are basically of no use.  You would be better to increase your overflow, or surface agitation or something like that.  Think about those airstones in freshwater tanks.  The airstones don't provide much O2 to the water.... but where they ripple the water at the top, that does provide O2 and that is why they are useful.

As for Marcus's comments, mostly on target.  It isn't really backwards at night, so much as they aren't undergoing photosynthesis so their respiration is "seen" and not "covered up".  The refugia doesn't keep pH up by producing oxygen but actually by removing the CO2.  More of a technicality becuase most people don't really care why it works, as long as it works.

One last idea.  I believe you are better to simply drop your tank temp from 80 (or whatever it is) to 75.  To me, that makes a big difference.

Adam 

Hey, I just posted this in a different place! In with the good, out
with the bad!

How do you make "osmosis" a verb?

Jon, do you think airbubblers are better than powerheads for air
exchange? I've always thought powerheads are like placing a patient
on a ventilator, a mechanical way of improving his lung function/air
exchange. His lungs can't keep up with the co2 his body is making,
and the mechanical ventilation helps him "blow" it off. And, an
airstone is like putting a patient on a nasal cannula, a little extra o2
which might raise his oxygen level, but really can't help him get rid
of excess co2.

Unless the bubbler was really pulling water up........Wouldn't that
take a whole lot o' bubbles?

Adam Blundell wrote: One last idea.  I believe you are better to simply drop your tank temp from 80 (or whatever it is) to 75.  To me, that makes a big difference.

I agree 100%!  That'll make a big difference.

We can all agree that gas exchange occurs at the air and water boundry.  Now think of all those tiny bubbles as little packets of air (which of course they are).  All those little sphere's have lots and lots of surface area.  For example, a 1 inch column of tiny air bubbles located 10 inches below the surface has about the same surface area as the whole top area of a 55 gallon tank.  And all those little bubbles replace themselves every couple seconds!  You still need to move the "exchanged" water away and bring in new "unexchanged" water.

Suzy, if you do, expect a lot of salt creep where the bubbles surface and break.  That's the drawback.  And I wasn't really advocating there use, just explaining why I think they work.  Do you have a skimmer?  It does essentually the same thing without the creep.

I understand gas exchange as Jon explained it. The rate at which the dissolved gases in the water can reach equilibrium with the atmosphere depends in part on the surface area between the air and the water. Airstones bubbling in the water adds a lot of surface area across which CO2 can be "blown off" and O2 can be absorbed by the water. Water pumps help by increasing the amount of water which contacts the air to exchange gas with the atmosphere.

-Tom