# CO2 vs. water movement



## joesaysso (Jun 4, 2011)

A few years ago, I had a 29 gallon tank where I could seemingly grow anything I put into it. If I didn't prune at least every two weeks, the plants would get so thick that the fish would be totally invisible in the tank; lost amongst the thick leaves and intertwining stems. All of that early success really got me hooked on plants. However, all of that success came at a time in my life when I was home more often. A few years past, and I was suddenly on the road working more often. All of that time away left the plants in the hands of my wife, who doesn't really have the time to take care of them. And of course after a while, they eventually died off. Now I'm at a point where I expect to be home more often and I'm ready to jump back in again. This time however, I movin on up and planting my 150. 

I've always known that a bit of water movement in the tank was essential to spread nutrients to the plants all over the tank. However, I've also known that any surface agitation causes loss of CO2. In the past, I've always considered CO2 to be more important and had kept my tanks as still as possible.

Lately however, as I have been lurking on the site prior to posting, I've seen some pics of tanks where the water level is a bit lower. This, I am assuming, is to use the filter outlet as a way to get the water moving in the tank. This method causes much surface agitation. I've also seen videos where people would say that there should be enough movment that all of the plants have a gentle sway. My plants never swayed with the exception of the ones that were next to/under the filter. But being that this tank is in the living room, essentially my show tank, I want to make sure I'm covering all of my bases.

So, finally to my question(s) here, how do you successfully balance out the two? Is the loss of CO2 not that great from surface agitation? Submersible power heads placed below the surface may not cause as much loss of CO2, but more equipment is a bit unsightful. Plus, as the plants get taller, getting stuck on the intake of the power head or getting tossed around by the direct flow of the outlet of the power head is probably not good either. How do you manage the movement/CO2 balance in your tanks?

Joe


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## JustLikeAPill (Oct 9, 2006)

You can have good water movement ( all the plants are gently moving ) while still having low surface agitation.

You want some surface movement, but not agitation, does that make sense? This allows oxygenation with minimal Co2 loss. It shouldn't be totally still. 

A good guide line is you want a turn over rate of 5-10X your volume water. This helps distribute CO2, nutrients, and pickup debris so your canister can catch it. Laminar flow helps.

You are usng a canister right?


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## joesaysso (Jun 4, 2011)

Indeed, I am using a canister filter. I have two "outlets" on the tank. The canister outlet and the CO2 outlet. The CO2 outlet is a bit higher in the tank. Its just a plastic tube that hangs on the back. The outlet sits about 2-3 inches below the surface. 

The outlet for the canister sits just a few inches below that maybe 6-8 inches below the surface. Obviously, the canister's outlet is more powerful than the CO2, as the CO2 is powered by a powerhead. The canister outlet produces a great deal of surface agitation when the water is low enough to expose it. 

I have both outlets on opposite ends of the tank to push water in different directions. When I do my water changes, I usually fill the tank to the brim, roughly 2 inches above the outlet for the CO2. This, in my head, is to keep as much CO2 in the tank as possible and not disturb the surface. Another thing worthy of noting is that the tank is a 150 tall. Its very deep at nearly 31 inches from top to bottom.

And yes, I get what you are saying as far as surface movement compared to agitation. However, I thought that one of the functions of healthy plants was that they give off plenty of oxygen, much more so than a little surface movement would provide. At the end of the day before lights out, the surface of the water has 1000s of bubbles on it given off by the leaves of the Amazon Swords. This is what I believed where my tanks oxygen was coming from.

Perhaps I am misunderstanding something though. I come into this thread distinguishing water surface movement and water column movement as seperate entities. Water column movement being to distribute nutrients to plants and assist in filtering and water surface movement for the purpose of oxygen exchange for the fish. However, the way I always understood things was when you have a planted tank, you wanted column movement not surface movement since surface movement wastes CO2 at the expensive of providing oxygen. Oxygen which would be provided by the plants anyway if they were healthy enough. Am I off the mark here?


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## niko (Jan 28, 2004)

I have experimented with reducing the surface movement to virtually nothing. The result is a disaster.

And really - in Nature there is rarely such a body of water. The surface always moves. If it doesn't you are looking at a rotting, stinky pond. Or it is an area connected to another one that has good water movement (surface and water column).

I've grown to believe that surface agitation is extremely important. It is not only about CO2 and Oxygen exchange. 

So, the goal here is to have as much surface agitation as possible without losing ungodly amounts of CO2 in the process. How much is just right you have to figure out for your own tank.

I got to say a word about your two outlets. I think it will be helpful with your decision what to do. What I'm about to say is simple, very simple. Yet most of us neglect it all the time: 

The purpose of the filter is to suck dirt from the tank, retain it, and process it into something less toxic. The efficiency of all that depends on how much "stuff" the filter can suck in. Looking closer at your tank you may notice that the water does not really carry ALL dirt particles toward the filter suction. Some particles just lay there, others aimlessly move around inside the tank and never make it to the suction. That's because your flow is all not directed toward the filter suction. All powerheads, pumps, additional outlets that confuse the direction of the main flow are not really helping you. My point is simple - make sure your flow is from outlet to inlet. AND it engages the entire body of water in your tank. Which means it needs to be quite large. 5x - 10x the tank volume per hour gives you a good idea. That will stir your surface too, no way you will keep it calm. 

That's it. Simple.

--Nikolay


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## joesaysso (Jun 4, 2011)

Hmmm.....perhaps some DIY spray bars off of the outlets of both the CO2 and the canister will aid in getting some movement further down the water column to achieve some actual circulation without buying more filters or pumps. Any thoughts?


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## davemonkey (Mar 29, 2008)

Also, (and if this was already mentioned I apologize, I only skimmed through the thread) make sure your outflow is opposite the CO2 output and it forces the CO2 down and around the tank. In other words, have the filter intake AND output at one end of the tank, and have the flow directed at the opposite end of the tank where it will hit the CO2, push against the glass at that end, and be forced downward and then back to your filter's intake. That way you have have as much surface agitation as you need and all you CO2 is still flowing through the water column with the water flowing back to your filter intake...passing by all the plants in the tank (ideally).


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## MonoBarrientos (Sep 29, 2010)

joesaysso said:


> Indeed, I am using a canister filter. I have two "outlets" on the tank. The canister outlet and the CO2 outlet. The CO2 outlet is a bit higher in the tank. Its just a plastic tube that hangs on the back. The outlet sits about 2-3 inches below the surface.
> 
> The outlet for the canister sits just a few inches below that maybe 6-8 inches below the surface. Obviously, the canister's outlet is more powerful than the CO2, as the CO2 is powered by a powerhead. The canister outlet produces a great deal of surface agitation when the water is low enough to expose it.
> 
> ...


Hi
Plants only contributes with the oxigenation (as "biologycal factor", the o2 as a subproduct of Hill´reaction), but the most direct way of oxygenation, is the "physical" factor: surface movement, because in comparison with "static" water, the contact área between air and water increases dramatically in a same interval period, and the interchange of gases happens.

Bad circulation and mynimal surface movement can be produce low level of O2 in relation for fauna and microfauna, even in a very-very planted tank (photosintesis alone is not always enought)

In my opinion is important to understand this.

Looses co2 with surface movement is a normal fact (that is GOOD, no bad, because prevends the acumulation), and only looses the "non-disolved" part. There is an equilibriom between disolved and non-dissolved part of the gas in the watter.

SO, In practice, is very simply: good disolution of co2 and good movement in the surface (excess is not neccesary) , that garantized good levels of O2 and CO2 , that´s all  . Is important to keep both levels optimal. Co2 no excludes O2, and both gasses are necessary in a healthy aquarium

Many hobbist (included experimented aquarists) says and recomended "no movement or mynimal move of the surface for no loose co2", in my opinion that recomendation is a mistake, without real foundament

"Saludos" from Chile


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## joesaysso (Jun 4, 2011)

Thank you, Mono and everybody else. I think I get a good amount of dissolved CO2 in the water. I rarely ever see any bubbles come out of the outflow. Its mostly a solid stream of water. The CO2 mixes with water inside a reactor underneath the tank and I suppose it does a really good job.

I will press on with my spray bar idea. I'll make a DIY spray bar as the outflow for my filter and let it be that way. I should get some good movement in the whole water column with a verticle bar off of the filter. I'm mineralizing some soil now. With the new subtrate and adjustments to the tank, I hope to have solid results in the coming weeks.


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## Dave-H (Oct 5, 2010)

I found that not much actual 'agitation' of the surface is necessary to keep O2 levels up, and if the surface is rippling too much you lose CO2 at a ridiculous rate. At least that's how it is in my tank.

I like to keep a very slight ripple on the surface, almost imperceptible. But, there is some good motion as when a leaf or something floats to the surface it will gently cruise around for around. I have quite a lot of current in the tank, but a very calm and gentle motion on the surface and it seems to work well.


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