Confused about surface agitation? - The Planted Tank Forum
Old 08-06-2011, 03:29 PM Thread Starter
Algae Grower

Join Date: Aug 2011
Location: England
Posts: 52

Im a bit confused about surface agitation. So to my understandings surface adgitation is when you agitate the surface of the water to equalize the waters dissolved gases to the same level as the atmosphere. So i were thinking if this is so then the water with an agitated surface should hold ~388ppm of CO2 since the atmosphere holds ~388ppm of CO2... And if this is true then adding extra CO2 to the water column for the plants to use in Photosynthesis, is unnecessary since there is already ~388ppm of Dissolved CO2 in the water. Or is my theory of agitated water surface is wrong if so correct me please .
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Old 08-06-2011, 03:54 PM
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The ratio of CO2 to other gases will be the same, but what's in your tank is mostly water, not gas. The amount of CO2 in the water will be very low. Something like 2-3ppm usually.
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Old 08-06-2011, 04:55 PM
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With plants in an aquarium and no CO2 added, the concentration of CO2 goes below what it would be in water without plants/algae, as it is consumed by them. Surface agitation helps remedy the depleted CO2 state that the water is in by exposing more of it to the air (just like stirring sugar into a drink helps it dissolve faster than simply letting it sit at the bottom.) That doesn't mean that the CO2 concentration will be the same in the air and in the water as its solubility in the two solutions (the gaseous solution that is the atmosphere and the liquid solution that is tank water) is very very different. This is even more pronounced with something like oxygen, which dissolves wretchedly badly in water, so much so that it is 21% of the atmosphere but only 0.001% of water that is completely oxygen saturated.

If you're adding CO2 to a tank, then surface agitation tends to remove it from solution. Even so, it's typically desirable for you do have surface agitation to help break up films and keep oxygen levels high.

Another way to think of this is that if your idea were right, the water in an aquarium would be 78% nitrogen by weight, 21% oxygen, and 1% argon, with no room for the water left over.

ETA: elemental flub

Last edited by jasonpatterson; 08-06-2011 at 09:29 PM.
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Old 08-06-2011, 05:37 PM Thread Starter
Algae Grower

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Location: England
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Thanks thats cleared alot up for me.
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Old 08-07-2011, 11:09 AM
Planted Tank Guru

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Side note. Dont be afraid of off gassing. Surface agitation and or the addition of oxygen to the tank far outweighs the loss of somme c02.
Better fish, plant, and benefiiicial bacteria health

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Old 08-07-2011, 04:12 PM
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Quote:
Originally Posted by HD Blazingwolf View Post
Side note. Dont be afraid of off gassing. Surface agitation and or the addition of oxygen to the tank far outweighs the loss of somme c02.
Better fish, plant, and benefiiicial bacteria health
True Dat!!!!!!!!!!!!!!!!!!!!!

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Old 08-09-2011, 10:55 AM
Algae Grower

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Thanks... HD Blazingwolf...... This was a question I have been wresting with for some time.

What is your opinion of overflows to a wet dry filter in a planted tank? Does it more negatively impact the CO2 level in the tank and does the benefit of oxygenated water in the filter and the removal of surface scum outweigh the negatives?
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Old 08-09-2011, 12:55 PM
Planted Tank Obsessed

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388 PPM (part per million) in air is nothing.
Since air is far far lighter than water,
it contains far far less CO2 per volume than you expect.

1 cubic meter of air weights just around 1.2 kilogram.
388 PPM for 1.2 kilogram is just 465.6 milligrams.
I mean 1 cubic meter of air contains only about 465.6 milligrams of CO2.

Water? 1 cubic meter weight a ton (1,000 kilograms)!

All that 465.6 milligrams of CO2 can make just about
0.4656 PPM for 1 cubic meter of water.
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Old 08-09-2011, 02:49 PM
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There are a lot of people here that use sumps with CO2 with good results from the added oxygen in the water but you need to keep the splashing or surface breaking movement to a minimum and with overflows surface scum can easily be eliminated.

But you can get similar results with canisters if you have good flow by means of circlulation pumps and air stones running after lights out.

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Old 08-09-2011, 10:06 PM
Algae Grower

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Thanks 150... BTW like the bike.

The main reason I quit using overflow was for the noise associated with the overflow and trickle filter. It was a bit irritating in my living room. The tank was originally a salt water setup. I was able to grow plants but never had the results that I frequently see here on the forum.

The good point for that setup was no pipes/ heaters etc. in the tank.
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Old 08-09-2011, 11:05 PM
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Thanks on the bike.

I like that look, I would rip out the overflows for a tank with a 360 degree view.

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Old 08-09-2011, 11:17 PM
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I use dual bio-wheels with a canister filter apart from the filter/CO2 setup. This is relatively quiet as long as the water level remains above the housing unit.

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Old 08-10-2011, 01:26 AM
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there was a writeup on a sump system that didn't affect c02 concentrations. sealing the sump is a great way to control off gassing as the c02 gas will reach equilibrium with the water in there as well.
i off gas pretty hard. my koralia points right at the surface of the water, i evaporate about a gallon every 2 days this way so i constantly have to refill or move the koralia to keep from blowing bubbles everywhere but its how my balance works.

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