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If airstones were so effective...

Ravenswing

Member
Joined
14 Dec 2012
Messages
153
Location
Finland
Hi!

Thinking of this ever lasting discussion of how effective aistone is when it comes to oxynating the water, why doesnt it add nitrogen to water along the oxygen? Air contains nitrogen 78% and oxygen 21% so if O2 were dissolved why not nitrogen? Is N so hardly dissolved...???

I personally don`t use airstones and don`t believe them adding oxygen thou they can make some flow. Or not. But as the complaining keeps going on from time to time, Id like to hear whats wrong with dissolving N if so.

Cheers,
 
It does dissolve nitrogen, being about 1/2 as soluble as oxygen, but cannot be used by plants or fish in this state. So makes no difference.
 
Hi all,
It does dissolve nitrogen, being about 1/2 as soluble as oxygen, but cannot be used by plants or fish in this state. So makes no difference.
Like Ian says nitrogen is a bit of a "Jekyll and Hyde" element. The N2 gas molecule is extremely stable, because the 2 N atoms are bound with a triple bond, it needs a lot of energy to split that bond (and a lot of energy is released, so TNT is trinitrotoluene, and KNO3 is an explosive as well as a fertiliser).

If you can break the bond, the single "fixed" nitrogen atom is highly reactive and will form, often soluble, compounds with nearly all other elements, carbon (example cyanide CN, again with a triple bond), oxygen (NO3), hydrogen (NH3) etc. The triple bond also means that nitrogen can help form complex molecules like the amino acids that form proteins. As you can see a lot of these compounds are far from inert or harmless.

So the inert N2 gas, which forms 79% of out atmosphere, is a very different entity from fixed nitrogen.

cheers Darrel
 
Most of the advantage of airstones in aerating a tank are actually down to them cirulating the water due to the rising stream of bubbles, not because of extra oxygen dissolving from the bubbles.

Also gases will only dissolve until they are in equilibrium with the water and the content of the bubble. For instance inject pure CO2 bubbles into a tank and it dissolves into the water until the water is saturated or the bubble reaches the surface. It will then come out of solution at the water's surface or into a drop checker. However the gas in a drop checker is in equilibrium with the gas dissolved in the tank water which is how they work. The bubbles of air produced by air stones are a little like this unless there is a real lack of oxygen or an excess of CO2 in the tank's water.
 
I certainly found running an airstone at night produces a "cleaner" tank and no surface film. I assume it is because it produces different flow patterns than the filters and power head and any dirt that has settled get moved into the water column and filtered away.
 
Hi all,
For instance inject pure CO2 bubbles into a tank and it dissolves into the water until the water is saturated or the bubble reaches the surface. It will then come out of solution at the water's surface or into a drop checker. However the gas in a drop checker is in equilibrium with the gas dissolved in the tank water which is how they work. The bubbles of air produced by air stones are a little like this unless there is a real lack of oxygen or an excess of CO2 in the tank's water.
Just like Ed says, another problem is that oxygen is less soluble than CO2, this means to get much diffusion of O2 from the bubbles they need to be extremely small (because of the surface area to volume ratio) and have a very long residence time in the water column. It is possible to do this, but having a filter with a very large gas exchange surface (like a wet and dry trickle filter) is much more cost effective option.

Have a look a this link: "Aeration and dissolved oxygen in the aquarium": <plecoplanet: Aeration and dissolved oxygen in the aquarium>.

cheers Darrel
 
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